X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopUnrollPass.cpp;h=d1daaa684ad1954d5a08652e77246c72d2c27651;hb=6a1227657333bf6a38924cda18d4b3bc677fc560;hp=22dd65c7cf69094b21d05c3797d5d0e14ac97f71;hpb=f0644b42a7947d5a4a57682b10edce631a80f36b;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/LoopUnrollPass.cpp b/lib/Transforms/Scalar/LoopUnrollPass.cpp index 22dd65c7cf6..d1daaa684ad 100644 --- a/lib/Transforms/Scalar/LoopUnrollPass.cpp +++ b/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -13,9 +13,12 @@ //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/CodeMetrics.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/Analysis/ScalarEvolutionExpressions.h" #include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DiagnosticInfo.h" @@ -26,6 +29,8 @@ #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Transforms/Utils/UnrollLoop.h" +#include "llvm/IR/InstVisitor.h" +#include "llvm/Analysis/InstructionSimplify.h" #include using namespace llvm; @@ -36,6 +41,22 @@ static cl::opt UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden, cl::desc("The cut-off point for automatic loop unrolling")); +static cl::opt UnrollMaxIterationsCountToAnalyze( + "unroll-max-iteration-count-to-analyze", cl::init(1000), cl::Hidden, + cl::desc("Don't allow loop unrolling to simulate more than this number of" + "iterations when checking full unroll profitability")); + +static cl::opt UnrollMinPercentOfOptimized( + "unroll-percent-of-optimized-for-complete-unroll", cl::init(20), cl::Hidden, + cl::desc("If complete unrolling could trigger further optimizations, and, " + "by that, remove the given percent of instructions, perform the " + "complete unroll even if it's beyond the threshold")); + +static cl::opt UnrollAbsoluteThreshold( + "unroll-absolute-threshold", cl::init(2000), cl::Hidden, + cl::desc("Don't unroll if the unrolled size is bigger than this threshold," + " even if we can remove big portion of instructions later.")); + static cl::opt UnrollCount("unroll-count", cl::init(0), cl::Hidden, cl::desc("Use this unroll count for all loops including those with " @@ -61,11 +82,16 @@ namespace { static char ID; // Pass ID, replacement for typeid LoopUnroll(int T = -1, int C = -1, int P = -1, int R = -1) : LoopPass(ID) { CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T); + CurrentAbsoluteThreshold = UnrollAbsoluteThreshold; + CurrentMinPercentOfOptimized = UnrollMinPercentOfOptimized; CurrentCount = (C == -1) ? UnrollCount : unsigned(C); CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P; CurrentRuntime = (R == -1) ? UnrollRuntime : (bool)R; UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0); + UserAbsoluteThreshold = (UnrollAbsoluteThreshold.getNumOccurrences() > 0); + UserPercentOfOptimized = + (UnrollMinPercentOfOptimized.getNumOccurrences() > 0); UserAllowPartial = (P != -1) || (UnrollAllowPartial.getNumOccurrences() > 0); UserRuntime = (R != -1) || (UnrollRuntime.getNumOccurrences() > 0); @@ -89,10 +115,16 @@ namespace { unsigned CurrentCount; unsigned CurrentThreshold; + unsigned CurrentAbsoluteThreshold; + unsigned CurrentMinPercentOfOptimized; bool CurrentAllowPartial; bool CurrentRuntime; bool UserCount; // CurrentCount is user-specified. bool UserThreshold; // CurrentThreshold is user-specified. + bool UserAbsoluteThreshold; // CurrentAbsoluteThreshold is + // user-specified. + bool UserPercentOfOptimized; // CurrentMinPercentOfOptimized is + // user-specified. bool UserAllowPartial; // CurrentAllowPartial is user-specified. bool UserRuntime; // CurrentRuntime is user-specified. @@ -102,15 +134,16 @@ namespace { /// loop preheaders be inserted into the CFG... /// void getAnalysisUsage(AnalysisUsage &AU) const override { - AU.addRequired(); - AU.addPreserved(); + AU.addRequired(); + AU.addRequired(); + AU.addPreserved(); AU.addRequiredID(LoopSimplifyID); AU.addPreservedID(LoopSimplifyID); AU.addRequiredID(LCSSAID); AU.addPreservedID(LCSSAID); AU.addRequired(); AU.addPreserved(); - AU.addRequired(); + AU.addRequired(); // FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info. // If loop unroll does not preserve dom info then LCSSA pass on next // loop will receive invalid dom info. @@ -123,6 +156,8 @@ namespace { void getUnrollingPreferences(Loop *L, const TargetTransformInfo &TTI, TargetTransformInfo::UnrollingPreferences &UP) { UP.Threshold = CurrentThreshold; + UP.AbsoluteThreshold = CurrentAbsoluteThreshold; + UP.MinPercentOfOptimized = CurrentMinPercentOfOptimized; UP.OptSizeThreshold = OptSizeUnrollThreshold; UP.PartialThreshold = CurrentThreshold; UP.PartialOptSizeThreshold = OptSizeUnrollThreshold; @@ -149,13 +184,33 @@ namespace { // unrolled loops respectively. void selectThresholds(const Loop *L, bool HasPragma, const TargetTransformInfo::UnrollingPreferences &UP, - unsigned &Threshold, unsigned &PartialThreshold) { + unsigned &Threshold, unsigned &PartialThreshold, + unsigned NumberOfOptimizedInstructions) { // Determine the current unrolling threshold. While this is // normally set from UnrollThreshold, it is overridden to a // smaller value if the current function is marked as // optimize-for-size, and the unroll threshold was not user // specified. Threshold = UserThreshold ? CurrentThreshold : UP.Threshold; + + // If we are allowed to completely unroll if we can remove M% of + // instructions, and we know that with complete unrolling we'll be able + // to kill N instructions, then we can afford to completely unroll loops + // with unrolled size up to N*100/M. + // Adjust the threshold according to that: + unsigned PercentOfOptimizedForCompleteUnroll = + UserPercentOfOptimized ? CurrentMinPercentOfOptimized + : UP.MinPercentOfOptimized; + unsigned AbsoluteThreshold = UserAbsoluteThreshold + ? CurrentAbsoluteThreshold + : UP.AbsoluteThreshold; + if (PercentOfOptimizedForCompleteUnroll) + Threshold = std::max(Threshold, + NumberOfOptimizedInstructions * 100 / + PercentOfOptimizedForCompleteUnroll); + // But don't allow unrolling loops bigger than absolute threshold. + Threshold = std::min(Threshold, AbsoluteThreshold); + PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold; if (!UserThreshold && L->getHeader()->getParent()->getAttributes(). @@ -181,8 +236,9 @@ namespace { char LoopUnroll::ID = 0; INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false) -INITIALIZE_AG_DEPENDENCY(TargetTransformInfo) -INITIALIZE_PASS_DEPENDENCY(LoopInfo) +INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) INITIALIZE_PASS_DEPENDENCY(LoopSimplify) INITIALIZE_PASS_DEPENDENCY(LCSSA) INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) @@ -197,14 +253,358 @@ Pass *llvm::createSimpleLoopUnrollPass() { return llvm::createLoopUnrollPass(-1, -1, 0, 0); } +static bool isLoadFromConstantInitializer(Value *V) { + if (GlobalVariable *GV = dyn_cast(V)) + if (GV->isConstant() && GV->hasDefinitiveInitializer()) + return GV->getInitializer(); + return false; +} + +struct FindConstantPointers { + bool LoadCanBeConstantFolded; + bool IndexIsConstant; + APInt Step; + APInt StartValue; + Value *BaseAddress; + const Loop *L; + ScalarEvolution &SE; + FindConstantPointers(const Loop *loop, ScalarEvolution &SE) + : LoadCanBeConstantFolded(true), IndexIsConstant(true), L(loop), SE(SE) {} + + bool follow(const SCEV *S) { + if (const SCEVUnknown *SC = dyn_cast(S)) { + // We've reached the leaf node of SCEV, it's most probably just a + // variable. Now it's time to see if it corresponds to a global constant + // global (in which case we can eliminate the load), or not. + BaseAddress = SC->getValue(); + LoadCanBeConstantFolded = + IndexIsConstant && isLoadFromConstantInitializer(BaseAddress); + return false; + } + if (isa(S)) + return true; + if (const SCEVAddRecExpr *AR = dyn_cast(S)) { + // If the current SCEV expression is AddRec, and its loop isn't the loop + // we are about to unroll, then we won't get a constant address after + // unrolling, and thus, won't be able to eliminate the load. + if (AR->getLoop() != L) + return IndexIsConstant = false; + // If the step isn't constant, we won't get constant addresses in unrolled + // version. Bail out. + if (const SCEVConstant *StepSE = + dyn_cast(AR->getStepRecurrence(SE))) + Step = StepSE->getValue()->getValue(); + else + return IndexIsConstant = false; + + return IndexIsConstant; + } + // If Result is true, continue traversal. + // Otherwise, we have found something that prevents us from (possible) load + // elimination. + return IndexIsConstant; + } + bool isDone() const { return !IndexIsConstant; } +}; + +// This class is used to get an estimate of the optimization effects that we +// could get from complete loop unrolling. It comes from the fact that some +// loads might be replaced with concrete constant values and that could trigger +// a chain of instruction simplifications. +// +// E.g. we might have: +// int a[] = {0, 1, 0}; +// v = 0; +// for (i = 0; i < 3; i ++) +// v += b[i]*a[i]; +// If we completely unroll the loop, we would get: +// v = b[0]*a[0] + b[1]*a[1] + b[2]*a[2] +// Which then will be simplified to: +// v = b[0]* 0 + b[1]* 1 + b[2]* 0 +// And finally: +// v = b[1] +class UnrollAnalyzer : public InstVisitor { + typedef InstVisitor Base; + friend class InstVisitor; + + const Loop *L; + unsigned TripCount; + ScalarEvolution &SE; + const TargetTransformInfo &TTI; + + DenseMap SimplifiedValues; + DenseMap LoadBaseAddresses; + SmallPtrSet CountedInstructions; + + /// \brief Count the number of optimized instructions. + unsigned NumberOfOptimizedInstructions; + + // Provide base case for our instruction visit. + bool visitInstruction(Instruction &I) { return false; }; + // TODO: We should also visit ICmp, FCmp, GetElementPtr, Trunc, ZExt, SExt, + // FPTrunc, FPExt, FPToUI, FPToSI, UIToFP, SIToFP, BitCast, Select, + // ExtractElement, InsertElement, ShuffleVector, ExtractValue, InsertValue. + // + // Probaly it's worth to hoist the code for estimating the simplifications + // effects to a separate class, since we have a very similar code in + // InlineCost already. + bool visitBinaryOperator(BinaryOperator &I) { + Value *LHS = I.getOperand(0), *RHS = I.getOperand(1); + if (!isa(LHS)) + if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) + LHS = SimpleLHS; + if (!isa(RHS)) + if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) + RHS = SimpleRHS; + Value *SimpleV = nullptr; + if (auto FI = dyn_cast(&I)) + SimpleV = + SimplifyFPBinOp(I.getOpcode(), LHS, RHS, FI->getFastMathFlags()); + else + SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS); + + if (SimpleV && CountedInstructions.insert(&I).second) + NumberOfOptimizedInstructions += TTI.getUserCost(&I); + + if (Constant *C = dyn_cast_or_null(SimpleV)) { + SimplifiedValues[&I] = C; + return true; + } + return false; + } + + Constant *computeLoadValue(LoadInst *LI, unsigned Iteration) { + if (!LI) + return nullptr; + Value *BaseAddr = LoadBaseAddresses[LI]; + if (!BaseAddr) + return nullptr; + + auto GV = dyn_cast(BaseAddr); + if (!GV) + return nullptr; + + ConstantDataSequential *CDS = + dyn_cast(GV->getInitializer()); + if (!CDS) + return nullptr; + + const SCEV *BaseAddrSE = SE.getSCEV(BaseAddr); + const SCEV *S = SE.getSCEV(LI->getPointerOperand()); + const SCEV *OffSE = SE.getMinusSCEV(S, BaseAddrSE); + + APInt StepC, StartC; + const SCEVAddRecExpr *AR = dyn_cast(OffSE); + if (!AR) + return nullptr; + + if (const SCEVConstant *StepSE = + dyn_cast(AR->getStepRecurrence(SE))) + StepC = StepSE->getValue()->getValue(); + else + return nullptr; + + if (const SCEVConstant *StartSE = dyn_cast(AR->getStart())) + StartC = StartSE->getValue()->getValue(); + else + return nullptr; + + unsigned ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U; + unsigned Start = StartC.getLimitedValue(); + unsigned Step = StepC.getLimitedValue(); + + unsigned Index = (Start + Step * Iteration) / ElemSize; + if (Index >= CDS->getNumElements()) + return nullptr; + + Constant *CV = CDS->getElementAsConstant(Index); + + return CV; + } + +public: + UnrollAnalyzer(const Loop *L, unsigned TripCount, ScalarEvolution &SE, + const TargetTransformInfo &TTI) + : L(L), TripCount(TripCount), SE(SE), TTI(TTI), + NumberOfOptimizedInstructions(0) {} + + // Visit all loads the loop L, and for those that, after complete loop + // unrolling, would have a constant address and it will point to a known + // constant initializer, record its base address for future use. It is used + // when we estimate number of potentially simplified instructions. + void findConstFoldableLoads() { + for (auto BB : L->getBlocks()) { + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { + if (LoadInst *LI = dyn_cast(I)) { + if (!LI->isSimple()) + continue; + Value *AddrOp = LI->getPointerOperand(); + const SCEV *S = SE.getSCEV(AddrOp); + FindConstantPointers Visitor(L, SE); + SCEVTraversal T(Visitor); + T.visitAll(S); + if (Visitor.IndexIsConstant && Visitor.LoadCanBeConstantFolded) { + LoadBaseAddresses[LI] = Visitor.BaseAddress; + } + } + } + } + } + + // Given a list of loads that could be constant-folded (LoadBaseAddresses), + // estimate number of optimized instructions after substituting the concrete + // values for the given Iteration. + // Fill in SimplifiedValues map for future use in DCE-estimation. + unsigned estimateNumberOfSimplifiedInstructions(unsigned Iteration) { + SmallVector Worklist; + SimplifiedValues.clear(); + CountedInstructions.clear(); + NumberOfOptimizedInstructions = 0; + + // We start by adding all loads to the worklist. + for (auto &LoadDescr : LoadBaseAddresses) { + LoadInst *LI = LoadDescr.first; + SimplifiedValues[LI] = computeLoadValue(LI, Iteration); + if (CountedInstructions.insert(LI).second) + NumberOfOptimizedInstructions += TTI.getUserCost(LI); + + for (User *U : LI->users()) { + Instruction *UI = dyn_cast(U); + if (!UI) + continue; + if (!L->contains(UI)) + continue; + Worklist.push_back(UI); + } + } + + // And then we try to simplify every user of every instruction from the + // worklist. If we do simplify a user, add it to the worklist to process + // its users as well. + while (!Worklist.empty()) { + Instruction *I = Worklist.pop_back_val(); + if (!visit(I)) + continue; + for (User *U : I->users()) { + Instruction *UI = dyn_cast(U); + if (!UI) + continue; + if (!L->contains(UI)) + continue; + Worklist.push_back(UI); + } + } + return NumberOfOptimizedInstructions; + } + + // Given a list of potentially simplifed instructions, estimate number of + // instructions that would become dead if we do perform the simplification. + unsigned estimateNumberOfDeadInstructions() { + NumberOfOptimizedInstructions = 0; + + // We keep a set vector for the worklist so that we don't wast space in the + // worklist queuing up the same instruction repeatedly. This can happen due + // to multiple operands being the same instruction or due to the same + // instruction being an operand of lots of things that end up dead or + // simplified. + SmallSetVector Worklist; + + // The dead instructions are held in a separate set. This is used to + // prevent us from re-examining instructions and make sure we only count + // the benifit once. The worklist's internal set handles insertion + // deduplication. + SmallPtrSet DeadInstructions; + + // Lambda to enque operands onto the worklist. + auto EnqueueOperands = [&](Instruction &I) { + for (auto *Op : I.operand_values()) + if (auto *OpI = dyn_cast(Op)) + Worklist.insert(OpI); + }; + + // Start by initializing worklist with simplified instructions. + for (auto &FoldedKeyValue : SimplifiedValues) + if (auto *FoldedInst = dyn_cast(FoldedKeyValue.first)) { + DeadInstructions.insert(FoldedInst); + + // Add each instruction operand of this dead instruction to the + // worklist. + EnqueueOperands(*FoldedInst); + } + + // If a definition of an insn is only used by simplified or dead + // instructions, it's also dead. Check defs of all instructions from the + // worklist. + while (!Worklist.empty()) { + Instruction *I = Worklist.pop_back_val(); + if (!L->contains(I)) + continue; + if (DeadInstructions.count(I)) + continue; + if (I->getNumUses() == 0) + continue; + bool AllUsersFolded = true; + for (User *U : I->users()) { + Instruction *UI = dyn_cast(U); + if (!SimplifiedValues[UI] && !DeadInstructions.count(UI)) { + AllUsersFolded = false; + break; + } + } + if (AllUsersFolded) { + NumberOfOptimizedInstructions += TTI.getUserCost(I); + DeadInstructions.insert(I); + EnqueueOperands(*I); + } + } + return NumberOfOptimizedInstructions; + } +}; + +// Complete loop unrolling can make some loads constant, and we need to know if +// that would expose any further optimization opportunities. +// This routine estimates this optimization effect and returns the number of +// instructions, that potentially might be optimized away. +static unsigned +approximateNumberOfOptimizedInstructions(const Loop *L, ScalarEvolution &SE, + unsigned TripCount, + const TargetTransformInfo &TTI) { + if (!TripCount || !UnrollMaxIterationsCountToAnalyze) + return 0; + + UnrollAnalyzer UA(L, TripCount, SE, TTI); + UA.findConstFoldableLoads(); + + // Estimate number of instructions, that could be simplified if we replace a + // load with the corresponding constant. Since the same load will take + // different values on different iterations, we have to go through all loop's + // iterations here. To limit ourselves here, we check only first N + // iterations, and then scale the found number, if necessary. + unsigned IterationsNumberForEstimate = + std::min(UnrollMaxIterationsCountToAnalyze, TripCount); + unsigned NumberOfOptimizedInstructions = 0; + for (unsigned i = 0; i < IterationsNumberForEstimate; ++i) { + NumberOfOptimizedInstructions += + UA.estimateNumberOfSimplifiedInstructions(i); + NumberOfOptimizedInstructions += UA.estimateNumberOfDeadInstructions(); + } + NumberOfOptimizedInstructions *= TripCount / IterationsNumberForEstimate; + + return NumberOfOptimizedInstructions; +} + /// ApproximateLoopSize - Approximate the size of the loop. static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, bool &NotDuplicatable, - const TargetTransformInfo &TTI) { + const TargetTransformInfo &TTI, + AssumptionCache *AC) { + SmallPtrSet EphValues; + CodeMetrics::collectEphemeralValues(L, AC, EphValues); + CodeMetrics Metrics; for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; ++I) - Metrics.analyzeBasicBlock(*I, TTI); + Metrics.analyzeBasicBlock(*I, TTI, EphValues); NumCalls = Metrics.NumInlineCandidates; NotDuplicatable = Metrics.notDuplicatable; @@ -212,8 +612,11 @@ static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, // Don't allow an estimate of size zero. This would allows unrolling of loops // with huge iteration counts, which is a compile time problem even if it's - // not a problem for code quality. - if (LoopSize == 0) LoopSize = 1; + // not a problem for code quality. Also, the code using this size may assume + // that each loop has at least three instructions (likely a conditional + // branch, a comparison feeding that branch, and some kind of loop increment + // feeding that comparison instruction). + LoopSize = std::max(LoopSize, 3u); return LoopSize; } @@ -221,48 +624,31 @@ static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, // Returns the loop hint metadata node with the given name (for example, // "llvm.loop.unroll.count"). If no such metadata node exists, then nullptr is // returned. -static const MDNode *GetUnrollMetadata(const Loop *L, StringRef Name) { - MDNode *LoopID = L->getLoopID(); - if (!LoopID) - return nullptr; - - // First operand should refer to the loop id itself. - assert(LoopID->getNumOperands() > 0 && "requires at least one operand"); - assert(LoopID->getOperand(0) == LoopID && "invalid loop id"); - - for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) { - const MDNode *MD = dyn_cast(LoopID->getOperand(i)); - if (!MD) - continue; - - const MDString *S = dyn_cast(MD->getOperand(0)); - if (!S) - continue; - - if (Name.equals(S->getString())) - return MD; - } +static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) { + if (MDNode *LoopID = L->getLoopID()) + return GetUnrollMetadata(LoopID, Name); return nullptr; } // Returns true if the loop has an unroll(full) pragma. static bool HasUnrollFullPragma(const Loop *L) { - return GetUnrollMetadata(L, "llvm.loop.unroll.full"); + return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full"); } // Returns true if the loop has an unroll(disable) pragma. static bool HasUnrollDisablePragma(const Loop *L) { - return GetUnrollMetadata(L, "llvm.loop.unroll.disable"); + return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.disable"); } // If loop has an unroll_count pragma return the (necessarily // positive) value from the pragma. Otherwise return 0. static unsigned UnrollCountPragmaValue(const Loop *L) { - const MDNode *MD = GetUnrollMetadata(L, "llvm.loop.unroll.count"); + MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count"); if (MD) { assert(MD->getNumOperands() == 2 && "Unroll count hint metadata should have two operands."); - unsigned Count = cast(MD->getOperand(1))->getZExtValue(); + unsigned Count = + mdconst::extract(MD->getOperand(1))->getZExtValue(); assert(Count >= 1 && "Unroll count must be positive."); return Count; } @@ -278,9 +664,9 @@ static void SetLoopAlreadyUnrolled(Loop *L) { if (!LoopID) return; // First remove any existing loop unrolling metadata. - SmallVector Vals; + SmallVector MDs; // Reserve first location for self reference to the LoopID metadata node. - Vals.push_back(nullptr); + MDs.push_back(nullptr); for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) { bool IsUnrollMetadata = false; MDNode *MD = dyn_cast(LoopID->getOperand(i)); @@ -288,17 +674,18 @@ static void SetLoopAlreadyUnrolled(Loop *L) { const MDString *S = dyn_cast(MD->getOperand(0)); IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll."); } - if (!IsUnrollMetadata) Vals.push_back(LoopID->getOperand(i)); + if (!IsUnrollMetadata) + MDs.push_back(LoopID->getOperand(i)); } // Add unroll(disable) metadata to disable future unrolling. LLVMContext &Context = L->getHeader()->getContext(); - SmallVector DisableOperands; + SmallVector DisableOperands; DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable")); MDNode *DisableNode = MDNode::get(Context, DisableOperands); - Vals.push_back(DisableNode); + MDs.push_back(DisableNode); - MDNode *NewLoopID = MDNode::get(Context, Vals); + MDNode *NewLoopID = MDNode::get(Context, MDs); // Set operand 0 to refer to the loop id itself. NewLoopID->replaceOperandWith(0, NewLoopID); L->setLoopID(NewLoopID); @@ -348,9 +735,13 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { if (skipOptnoneFunction(L)) return false; - LoopInfo *LI = &getAnalysis(); + Function &F = *L->getHeader()->getParent(); + + LoopInfo *LI = &getAnalysis().getLoopInfo(); ScalarEvolution *SE = &getAnalysis(); - const TargetTransformInfo &TTI = getAnalysis(); + const TargetTransformInfo &TTI = + getAnalysis().getTTI(F); + auto &AC = getAnalysis().getAssumptionCache(F); BasicBlock *Header = L->getHeader(); DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() @@ -369,13 +760,15 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { // Find trip count and trip multiple if count is not available unsigned TripCount = 0; unsigned TripMultiple = 1; - // Find "latch trip count". UnrollLoop assumes that control cannot exit - // via the loop latch on any iteration prior to TripCount. The loop may exit - // early via an earlier branch. - BasicBlock *LatchBlock = L->getLoopLatch(); - if (LatchBlock) { - TripCount = SE->getSmallConstantTripCount(L, LatchBlock); - TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock); + // If there are multiple exiting blocks but one of them is the latch, use the + // latch for the trip count estimation. Otherwise insist on a single exiting + // block for the trip count estimation. + BasicBlock *ExitingBlock = L->getLoopLatch(); + if (!ExitingBlock || !L->isLoopExiting(ExitingBlock)) + ExitingBlock = L->getExitingBlock(); + if (ExitingBlock) { + TripCount = SE->getSmallConstantTripCount(L, ExitingBlock); + TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock); } // Select an initial unroll count. This may be reduced later based @@ -387,9 +780,13 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { unsigned NumInlineCandidates; bool notDuplicatable; unsigned LoopSize = - ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI); + ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, &AC); DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); - uint64_t UnrolledSize = (uint64_t)LoopSize * Count; + + // When computing the unrolled size, note that the conditional branch on the + // backedge and the comparison feeding it are not replicated like the rest of + // the loop body (which is why 2 is subtracted). + uint64_t UnrolledSize = (uint64_t)(LoopSize-2) * Count + 2; if (notDuplicatable) { DEBUG(dbgs() << " Not unrolling loop which contains non-duplicatable" << " instructions.\n"); @@ -400,8 +797,14 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { return false; } + unsigned NumberOfOptimizedInstructions = + approximateNumberOfOptimizedInstructions(L, *SE, TripCount, TTI); + DEBUG(dbgs() << " Complete unrolling could save: " + << NumberOfOptimizedInstructions << "\n"); + unsigned Threshold, PartialThreshold; - selectThresholds(L, HasPragma, UP, Threshold, PartialThreshold); + selectThresholds(L, HasPragma, UP, Threshold, PartialThreshold, + NumberOfOptimizedInstructions); // Given Count, TripCount and thresholds determine the type of // unrolling which is to be performed. @@ -434,7 +837,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { } if (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) { // Reduce unroll count to be modulo of TripCount for partial unrolling. - Count = PartialThreshold / LoopSize; + Count = (std::max(PartialThreshold, 3u)-2) / (LoopSize-2); while (Count != 0 && TripCount % Count != 0) Count--; } @@ -448,7 +851,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { // the original count which satisfies the threshold limit. while (Count != 0 && UnrolledSize > PartialThreshold) { Count >>= 1; - UnrolledSize = LoopSize * Count; + UnrolledSize = (LoopSize-2) * Count + 2; } if (Count > UP.MaxCount) Count = UP.MaxCount; @@ -493,7 +896,8 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { } // Unroll the loop. - if (!UnrollLoop(L, Count, TripCount, AllowRuntime, TripMultiple, LI, this, &LPM)) + if (!UnrollLoop(L, Count, TripCount, AllowRuntime, TripMultiple, LI, this, + &LPM, &AC)) return false; return true;