X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopUnrollPass.cpp;h=37851ba87da3a7c0b20d868639ecb7f08a02b2eb;hp=90eb857c85e0ff799e4ac7b080ccf9276b0b90de;hb=2640fd5bae01dfdb7d07178c0a71cdbf8a519db6;hpb=b298db72531e607c4c4db31df3373f74a9b983b1 diff --git a/lib/Transforms/Scalar/LoopUnrollPass.cpp b/lib/Transforms/Scalar/LoopUnrollPass.cpp index 90eb857c85e..37851ba87da 100644 --- a/lib/Transforms/Scalar/LoopUnrollPass.cpp +++ b/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -12,38 +12,91 @@ // counts of loops easily. //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "loop-unroll" -#include "llvm/IntrinsicInst.h" #include "llvm/Transforms/Scalar.h" -#include "llvm/Analysis/LoopPass.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" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Metadata.h" #include "llvm/Support/CommandLine.h" #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; +#define DEBUG_TYPE "loop-unroll" + 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, for testing purposes")); + cl::desc("Use this unroll count for all loops including those with " + "unroll_count pragma values, for testing purposes")); static cl::opt UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden, cl::desc("Allows loops to be partially unrolled until " "-unroll-threshold loop size is reached.")); +static cl::opt +UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden, + cl::desc("Unroll loops with run-time trip counts")); + +static cl::opt +PragmaUnrollThreshold("pragma-unroll-threshold", cl::init(16 * 1024), cl::Hidden, + cl::desc("Unrolled size limit for loops with an unroll(full) or " + "unroll_count pragma.")); + namespace { class LoopUnroll : public LoopPass { public: static char ID; // Pass ID, replacement for typeid - LoopUnroll() : LoopPass(ID) { + 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); + UserCount = (C != -1) || (UnrollCount.getNumOccurrences() > 0); + initializeLoopUnrollPass(*PassRegistry::getPassRegistry()); } @@ -51,147 +104,800 @@ namespace { /// that the loop unroll should be performed regardless of how much /// code expansion would result. static const unsigned NoThreshold = UINT_MAX; - + // Threshold to use when optsize is specified (and there is no // explicit -unroll-threshold). static const unsigned OptSizeUnrollThreshold = 50; - + + // Default unroll count for loops with run-time trip count if + // -unroll-count is not set + static const unsigned UnrollRuntimeCount = 8; + + 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. - bool runOnLoop(Loop *L, LPPassManager &LPM); + bool runOnLoop(Loop *L, LPPassManager &LPM) override; /// This transformation requires natural loop information & requires that /// loop preheaders be inserted into the CFG... /// - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - AU.addRequired(); - AU.addPreserved(); + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired(); + AU.addRequired(); + AU.addPreserved(); AU.addRequiredID(LoopSimplifyID); AU.addPreservedID(LoopSimplifyID); AU.addRequiredID(LCSSAID); AU.addPreservedID(LCSSAID); + AU.addRequired(); AU.addPreserved(); + 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. // For now, recreate dom info, if loop is unrolled. - AU.addPreserved(); + AU.addPreserved(); + } + + // Fill in the UnrollingPreferences parameter with values from the + // TargetTransformationInfo. + 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; + UP.Count = CurrentCount; + UP.MaxCount = UINT_MAX; + UP.Partial = CurrentAllowPartial; + UP.Runtime = CurrentRuntime; + TTI.getUnrollingPreferences(L, UP); + } + + // Select and return an unroll count based on parameters from + // user, unroll preferences, unroll pragmas, or a heuristic. + // SetExplicitly is set to true if the unroll count is is set by + // the user or a pragma rather than selected heuristically. + unsigned + selectUnrollCount(const Loop *L, unsigned TripCount, bool PragmaFullUnroll, + unsigned PragmaCount, + const TargetTransformInfo::UnrollingPreferences &UP, + bool &SetExplicitly); + + // Select threshold values used to limit unrolling based on a + // total unrolled size. Parameters Threshold and PartialThreshold + // are set to the maximum unrolled size for fully and partially + // unrolled loops respectively. + void selectThresholds(const Loop *L, bool HasPragma, + const TargetTransformInfo::UnrollingPreferences &UP, + 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(). + hasAttribute(AttributeSet::FunctionIndex, + Attribute::OptimizeForSize)) { + Threshold = UP.OptSizeThreshold; + PartialThreshold = UP.PartialOptSizeThreshold; + } + if (HasPragma) { + // If the loop has an unrolling pragma, we want to be more + // aggressive with unrolling limits. Set thresholds to at + // least the PragmaTheshold value which is larger than the + // default limits. + if (Threshold != NoThreshold) + Threshold = std::max(Threshold, PragmaUnrollThreshold); + if (PartialThreshold != NoThreshold) + PartialThreshold = + std::max(PartialThreshold, PragmaUnrollThreshold); + } } }; } char LoopUnroll::ID = 0; INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false) -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) INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false) -Pass *llvm::createLoopUnrollPass() { return new LoopUnroll(); } +Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial, + int Runtime) { + return new LoopUnroll(Threshold, Count, AllowPartial, Runtime); +} + +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)) + if (!OpI->use_empty()) + 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; + 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) { +static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, + bool &NotDuplicatable, + 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); + Metrics.analyzeBasicBlock(*I, TTI, EphValues); NumCalls = Metrics.NumInlineCandidates; - + NotDuplicatable = Metrics.notDuplicatable; + unsigned LoopSize = Metrics.NumInsts; - - // If we can identify the induction variable, we know that it will become - // constant when we unroll the loop, so factor that into our loop size - // estimate. - // FIXME: We have to divide by InlineConstants::InstrCost because the - // measure returned by CountCodeReductionForConstant is not an instruction - // count, but rather a weight as defined by InlineConstants. It would - // probably be a good idea to standardize on a single weighting scheme by - // pushing more of the logic for weighting into CodeMetrics. - if (PHINode *IndVar = L->getCanonicalInductionVariable()) { - unsigned SizeDecrease = Metrics.CountCodeReductionForConstant(IndVar); - // NOTE: Because SizeDecrease is a fuzzy estimate, we don't want to allow - // it to totally negate the cost of unrolling a loop. - SizeDecrease = SizeDecrease > LoopSize / 2 ? LoopSize / 2 : SizeDecrease; - } - + // 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; } +// 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 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 GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full"); +} + +// Returns true if the loop has an unroll(disable) pragma. +static bool HasUnrollDisablePragma(const Loop *L) { + 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) { + MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count"); + if (MD) { + assert(MD->getNumOperands() == 2 && + "Unroll count hint metadata should have two operands."); + unsigned Count = + mdconst::extract(MD->getOperand(1))->getZExtValue(); + assert(Count >= 1 && "Unroll count must be positive."); + return Count; + } + return 0; +} + +// Remove existing unroll metadata and add unroll disable metadata to +// indicate the loop has already been unrolled. This prevents a loop +// from being unrolled more than is directed by a pragma if the loop +// unrolling pass is run more than once (which it generally is). +static void SetLoopAlreadyUnrolled(Loop *L) { + MDNode *LoopID = L->getLoopID(); + if (!LoopID) return; + + // First remove any existing loop unrolling metadata. + SmallVector MDs; + // Reserve first location for self reference to the LoopID metadata node. + MDs.push_back(nullptr); + for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) { + bool IsUnrollMetadata = false; + MDNode *MD = dyn_cast(LoopID->getOperand(i)); + if (MD) { + const MDString *S = dyn_cast(MD->getOperand(0)); + IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll."); + } + if (!IsUnrollMetadata) + MDs.push_back(LoopID->getOperand(i)); + } + + // Add unroll(disable) metadata to disable future unrolling. + LLVMContext &Context = L->getHeader()->getContext(); + SmallVector DisableOperands; + DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable")); + MDNode *DisableNode = MDNode::get(Context, DisableOperands); + MDs.push_back(DisableNode); + + MDNode *NewLoopID = MDNode::get(Context, MDs); + // Set operand 0 to refer to the loop id itself. + NewLoopID->replaceOperandWith(0, NewLoopID); + L->setLoopID(NewLoopID); +} + +unsigned LoopUnroll::selectUnrollCount( + const Loop *L, unsigned TripCount, bool PragmaFullUnroll, + unsigned PragmaCount, const TargetTransformInfo::UnrollingPreferences &UP, + bool &SetExplicitly) { + SetExplicitly = true; + + // User-specified count (either as a command-line option or + // constructor parameter) has highest precedence. + unsigned Count = UserCount ? CurrentCount : 0; + + // If there is no user-specified count, unroll pragmas have the next + // highest precendence. + if (Count == 0) { + if (PragmaCount) { + Count = PragmaCount; + } else if (PragmaFullUnroll) { + Count = TripCount; + } + } + + if (Count == 0) + Count = UP.Count; + + if (Count == 0) { + SetExplicitly = false; + if (TripCount == 0) + // Runtime trip count. + Count = UnrollRuntimeCount; + else + // Conservative heuristic: if we know the trip count, see if we can + // completely unroll (subject to the threshold, checked below); otherwise + // try to find greatest modulo of the trip count which is still under + // threshold value. + Count = TripCount; + } + if (TripCount && Count > TripCount) + return TripCount; + return Count; +} + bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { - LoopInfo *LI = &getAnalysis(); + if (skipOptnoneFunction(L)) + return false; + + Function &F = *L->getHeader()->getParent(); + + LoopInfo *LI = &getAnalysis().getLoopInfo(); + ScalarEvolution *SE = &getAnalysis(); + const TargetTransformInfo &TTI = + getAnalysis().getTTI(F); + auto &AC = getAnalysis().getAssumptionCache(F); BasicBlock *Header = L->getHeader(); DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() << "] Loop %" << Header->getName() << "\n"); - (void)Header; - - // 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. - CurrentThreshold = UnrollThreshold; - if (Header->getParent()->hasFnAttr(Attribute::OptimizeForSize) && - UnrollThreshold.getNumOccurrences() == 0) - CurrentThreshold = OptSizeUnrollThreshold; - - // Find trip count - unsigned TripCount = L->getSmallConstantTripCount(); - unsigned Count = UnrollCount; - - // Automatically select an unroll count. - if (Count == 0) { - // Conservative heuristic: if we know the trip count, see if we can - // completely unroll (subject to the threshold, checked below); otherwise - // try to find greatest modulo of the trip count which is still under - // threshold value. - if (TripCount == 0) - return false; - Count = TripCount; + + if (HasUnrollDisablePragma(L)) { + return false; + } + bool PragmaFullUnroll = HasUnrollFullPragma(L); + unsigned PragmaCount = UnrollCountPragmaValue(L); + bool HasPragma = PragmaFullUnroll || PragmaCount > 0; + + TargetTransformInfo::UnrollingPreferences UP; + getUnrollingPreferences(L, TTI, UP); + + // Find trip count and trip multiple if count is not available + unsigned TripCount = 0; + unsigned TripMultiple = 1; + // 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 + // on size thresholds. + bool CountSetExplicitly; + unsigned Count = selectUnrollCount(L, TripCount, PragmaFullUnroll, + PragmaCount, UP, CountSetExplicitly); + + unsigned NumInlineCandidates; + bool notDuplicatable; + unsigned LoopSize = + ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, &AC); + DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); + + // 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"); + return false; + } + if (NumInlineCandidates != 0) { + DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n"); + 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, + NumberOfOptimizedInstructions); + + // Given Count, TripCount and thresholds determine the type of + // unrolling which is to be performed. + enum { Full = 0, Partial = 1, Runtime = 2 }; + int Unrolling; + if (TripCount && Count == TripCount) { + if (Threshold != NoThreshold && UnrolledSize > Threshold) { + DEBUG(dbgs() << " Too large to fully unroll with count: " << Count + << " because size: " << UnrolledSize << ">" << Threshold + << "\n"); + Unrolling = Partial; + } else { + Unrolling = Full; + } + } else if (TripCount && Count < TripCount) { + Unrolling = Partial; + } else { + Unrolling = Runtime; } - // Enforce the threshold. - if (CurrentThreshold != NoThreshold) { - unsigned NumInlineCandidates; - unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates); - DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); - if (NumInlineCandidates != 0) { - DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n"); + // Reduce count based on the type of unrolling and the threshold values. + unsigned OriginalCount = Count; + bool AllowRuntime = UserRuntime ? CurrentRuntime : UP.Runtime; + if (Unrolling == Partial) { + bool AllowPartial = UserAllowPartial ? CurrentAllowPartial : UP.Partial; + if (!AllowPartial && !CountSetExplicitly) { + DEBUG(dbgs() << " will not try to unroll partially because " + << "-unroll-allow-partial not given\n"); return false; } - uint64_t Size = (uint64_t)LoopSize*Count; - if (TripCount != 1 && Size > CurrentThreshold) { - DEBUG(dbgs() << " Too large to fully unroll with count: " << Count - << " because size: " << Size << ">" << CurrentThreshold << "\n"); - if (!UnrollAllowPartial) { - DEBUG(dbgs() << " will not try to unroll partially because " - << "-unroll-allow-partial not given\n"); - return false; - } - // Reduce unroll count to be modulo of TripCount for partial unrolling - Count = CurrentThreshold / LoopSize; - while (Count != 0 && TripCount%Count != 0) { + if (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) { + // Reduce unroll count to be modulo of TripCount for partial unrolling. + Count = (std::max(PartialThreshold, 3u)-2) / (LoopSize-2); + while (Count != 0 && TripCount % Count != 0) Count--; + } + } else if (Unrolling == Runtime) { + if (!AllowRuntime && !CountSetExplicitly) { + DEBUG(dbgs() << " will not try to unroll loop with runtime trip count " + << "-unroll-runtime not given\n"); + return false; + } + // Reduce unroll count to be the largest power-of-two factor of + // the original count which satisfies the threshold limit. + while (Count != 0 && UnrolledSize > PartialThreshold) { + Count >>= 1; + UnrolledSize = (LoopSize-2) * Count + 2; + } + if (Count > UP.MaxCount) + Count = UP.MaxCount; + DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n"); + } + + if (HasPragma) { + if (PragmaCount != 0) + // If loop has an unroll count pragma mark loop as unrolled to prevent + // unrolling beyond that requested by the pragma. + SetLoopAlreadyUnrolled(L); + + // Emit optimization remarks if we are unable to unroll the loop + // as directed by a pragma. + DebugLoc LoopLoc = L->getStartLoc(); + Function *F = Header->getParent(); + LLVMContext &Ctx = F->getContext(); + if (PragmaFullUnroll && PragmaCount == 0) { + if (TripCount && Count != TripCount) { + emitOptimizationRemarkMissed( + Ctx, DEBUG_TYPE, *F, LoopLoc, + "Unable to fully unroll loop as directed by unroll(full) pragma " + "because unrolled size is too large."); + } else if (!TripCount) { + emitOptimizationRemarkMissed( + Ctx, DEBUG_TYPE, *F, LoopLoc, + "Unable to fully unroll loop as directed by unroll(full) pragma " + "because loop has a runtime trip count."); } - if (Count < 2) { - DEBUG(dbgs() << " could not unroll partially\n"); - return false; - } - DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n"); + } else if (PragmaCount > 0 && Count != OriginalCount) { + emitOptimizationRemarkMissed( + Ctx, DEBUG_TYPE, *F, LoopLoc, + "Unable to unroll loop the number of times directed by " + "unroll_count pragma because unrolled size is too large."); } } + if (Unrolling != Full && Count < 2) { + // Partial unrolling by 1 is a nop. For full unrolling, a factor + // of 1 makes sense because loop control can be eliminated. + return false; + } + // Unroll the loop. - Function *F = L->getHeader()->getParent(); - if (!UnrollLoop(L, Count, LI, &LPM)) + if (!UnrollLoop(L, Count, TripCount, AllowRuntime, TripMultiple, LI, this, + &LPM, &AC)) return false; - // FIXME: Reconstruct dom info, because it is not preserved properly. - if (DominatorTree *DT = getAnalysisIfAvailable()) - DT->runOnFunction(*F); return true; }