| //===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file 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. |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/CodeMetrics.h" |
| #include "llvm/Analysis/InstructionSimplify.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/InstVisitor.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 <climits> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "loop-unroll" |
| |
| static cl::opt<unsigned> |
| UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden, |
| cl::desc("The cut-off point for automatic loop unrolling")); |
| |
| static cl::opt<unsigned> UnrollMaxIterationsCountToAnalyze( |
| "unroll-max-iteration-count-to-analyze", cl::init(0), 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<unsigned> 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<unsigned> 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<unsigned> |
| UnrollCount("unroll-count", cl::init(0), cl::Hidden, |
| cl::desc("Use this unroll count for all loops including those with " |
| "unroll_count pragma values, for testing purposes")); |
| |
| static cl::opt<bool> |
| 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<bool> |
| UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden, |
| cl::desc("Unroll loops with run-time trip counts")); |
| |
| static cl::opt<unsigned> |
| 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(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()); |
| } |
| |
| /// A magic value for use with the Threshold parameter to indicate |
| /// 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) override; |
| |
| /// This transformation requires natural loop information & requires that |
| /// loop preheaders be inserted into the CFG... |
| /// |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<AssumptionCacheTracker>(); |
| AU.addRequired<LoopInfoWrapperPass>(); |
| AU.addPreserved<LoopInfoWrapperPass>(); |
| AU.addRequiredID(LoopSimplifyID); |
| AU.addPreservedID(LoopSimplifyID); |
| AU.addRequiredID(LCSSAID); |
| AU.addPreservedID(LCSSAID); |
| AU.addRequired<ScalarEvolution>(); |
| AU.addPreserved<ScalarEvolution>(); |
| AU.addRequired<TargetTransformInfoWrapperPass>(); |
| // 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<DominatorTreeWrapperPass>(); |
| } |
| |
| // 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; |
| UP.AllowExpensiveTripCount = false; |
| 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<unsigned>(Threshold, |
| NumberOfOptimizedInstructions * 100 / |
| PercentOfOptimizedForCompleteUnroll); |
| // But don't allow unrolling loops bigger than absolute threshold. |
| Threshold = std::min<unsigned>(Threshold, AbsoluteThreshold); |
| |
| PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold; |
| if (!UserThreshold && |
| L->getHeader()->getParent()->hasFnAttribute( |
| 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<unsigned>(Threshold, PragmaUnrollThreshold); |
| if (PartialThreshold != NoThreshold) |
| PartialThreshold = |
| std::max<unsigned>(PartialThreshold, PragmaUnrollThreshold); |
| } |
| } |
| }; |
| } |
| |
| char LoopUnroll::ID = 0; |
| INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false) |
| 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(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<GlobalVariable>(V)) |
| if (GV->isConstant() && GV->hasDefinitiveInitializer()) |
| return GV->getInitializer(); |
| return false; |
| } |
| |
| namespace { |
| 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<SCEVUnknown>(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<SCEVConstant>(S)) |
| return true; |
| if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(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<SCEVConstant>(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<UnrollAnalyzer, bool> { |
| typedef InstVisitor<UnrollAnalyzer, bool> Base; |
| friend class InstVisitor<UnrollAnalyzer, bool>; |
| |
| const Loop *L; |
| unsigned TripCount; |
| ScalarEvolution &SE; |
| const TargetTransformInfo &TTI; |
| |
| DenseMap<Value *, Constant *> SimplifiedValues; |
| DenseMap<LoadInst *, Value *> LoadBaseAddresses; |
| SmallPtrSet<Instruction *, 32> 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<Constant>(LHS)) |
| if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) |
| LHS = SimpleLHS; |
| if (!isa<Constant>(RHS)) |
| if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) |
| RHS = SimpleRHS; |
| Value *SimpleV = nullptr; |
| const DataLayout &DL = I.getModule()->getDataLayout(); |
| if (auto FI = dyn_cast<FPMathOperator>(&I)) |
| SimpleV = |
| SimplifyFPBinOp(I.getOpcode(), LHS, RHS, FI->getFastMathFlags(), DL); |
| else |
| SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS, DL); |
| |
| if (SimpleV && CountedInstructions.insert(&I).second) |
| NumberOfOptimizedInstructions += TTI.getUserCost(&I); |
| |
| if (Constant *C = dyn_cast_or_null<Constant>(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<GlobalVariable>(BaseAddr); |
| if (!GV) |
| return nullptr; |
| |
| ConstantDataSequential *CDS = |
| dyn_cast<ConstantDataSequential>(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<SCEVAddRecExpr>(OffSE); |
| if (!AR) |
| return nullptr; |
| |
| if (const SCEVConstant *StepSE = |
| dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE))) |
| StepC = StepSE->getValue()->getValue(); |
| else |
| return nullptr; |
| |
| if (const SCEVConstant *StartSE = dyn_cast<SCEVConstant>(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<LoadInst>(I)) { |
| if (!LI->isSimple()) |
| continue; |
| Value *AddrOp = LI->getPointerOperand(); |
| const SCEV *S = SE.getSCEV(AddrOp); |
| FindConstantPointers Visitor(L, SE); |
| SCEVTraversal<FindConstantPointers> 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. Also track how many instructions become |
| // dead through this process. |
| unsigned estimateNumberOfOptimizedInstructions(unsigned Iteration) { |
| // 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<Instruction *, 8> Worklist; |
| |
| // Clear the simplified values and counts for this iteration. |
| 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()) |
| Worklist.insert(cast<Instruction>(U)); |
| } |
| |
| // 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 (!L->contains(I)) |
| continue; |
| if (!visit(I)) |
| continue; |
| for (User *U : I->users()) |
| Worklist.insert(cast<Instruction>(U)); |
| } |
| |
| // Now that we know the potentially simplifed instructions, estimate number |
| // of instructions that would become dead if we do perform the |
| // simplification. |
| |
| // 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<Instruction *, 16> DeadInstructions; |
| |
| // Lambda to enque operands onto the worklist. |
| auto EnqueueOperands = [&](Instruction &I) { |
| for (auto *Op : I.operand_values()) |
| if (auto *OpI = dyn_cast<Instruction>(Op)) |
| if (!OpI->use_empty()) |
| Worklist.insert(OpI); |
| }; |
| |
| // Start by initializing worklist with simplified instructions. |
| for (auto &FoldedKeyValue : SimplifiedValues) |
| if (auto *FoldedInst = dyn_cast<Instruction>(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 (std::all_of(I->user_begin(), I->user_end(), [&](User *U) { |
| return DeadInstructions.count(cast<Instruction>(U)); |
| })) { |
| NumberOfOptimizedInstructions += TTI.getUserCost(I); |
| DeadInstructions.insert(I); |
| EnqueueOperands(*I); |
| } |
| } |
| return NumberOfOptimizedInstructions; |
| } |
| }; |
| } // namespace |
| |
| // 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<unsigned>(UnrollMaxIterationsCountToAnalyze, TripCount); |
| unsigned NumberOfOptimizedInstructions = 0; |
| for (unsigned i = 0; i < IterationsNumberForEstimate; ++i) |
| NumberOfOptimizedInstructions += |
| UA.estimateNumberOfOptimizedInstructions(i); |
| |
| 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, |
| AssumptionCache *AC) { |
| SmallPtrSet<const Value *, 32> 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, EphValues); |
| NumCalls = Metrics.NumInlineCandidates; |
| NotDuplicatable = Metrics.notDuplicatable; |
| |
| unsigned LoopSize = Metrics.NumInsts; |
| |
| // 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. 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"); |
| } |
| |
| // Returns true if the loop has an runtime unroll(disable) pragma. |
| static bool HasRuntimeUnrollDisablePragma(const Loop *L) { |
| return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.runtime.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<ConstantInt>(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<Metadata *, 4> 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<MDNode>(LoopID->getOperand(i)); |
| if (MD) { |
| const MDString *S = dyn_cast<MDString>(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<Metadata *, 1> 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) { |
| if (skipOptnoneFunction(L)) |
| return false; |
| |
| Function &F = *L->getHeader()->getParent(); |
| |
| LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| ScalarEvolution *SE = &getAnalysis<ScalarEvolution>(); |
| const TargetTransformInfo &TTI = |
| getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); |
| auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); |
| |
| BasicBlock *Header = L->getHeader(); |
| DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() |
| << "] Loop %" << Header->getName() << "\n"); |
| |
| 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; |
| } |
| |
| // Reduce count based on the type of unrolling and the threshold values. |
| unsigned OriginalCount = Count; |
| bool AllowRuntime = UserRuntime ? CurrentRuntime : UP.Runtime; |
| if (HasRuntimeUnrollDisablePragma(L)) { |
| AllowRuntime = false; |
| } |
| 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; |
| } |
| 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."); |
| } |
| } 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. |
| if (!UnrollLoop(L, Count, TripCount, AllowRuntime, UP.AllowExpensiveTripCount, |
| TripMultiple, LI, this, &LPM, &AC)) |
| return false; |
| |
| return true; |
| } |
