diff options
Diffstat (limited to 'llvm/lib/Transforms/Vectorize/LoopVectorize.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 1217 |
1 files changed, 1 insertions, 1216 deletions
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp index e57bcb6048f..8de6127721d 100644 --- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp +++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp @@ -58,6 +58,7 @@ #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/BlockFrequencyInfo.h" #include "llvm/Analysis/CodeMetrics.h" +#include "llvm/Analysis/LoopAccessAnalysis.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/LoopIterator.h" #include "llvm/Analysis/LoopPass.h" @@ -218,35 +219,6 @@ class LoopVectorizationLegality; class LoopVectorizationCostModel; class LoopVectorizeHints; -/// Optimization analysis message produced during vectorization. Messages inform -/// the user why vectorization did not occur. -class VectorizationReport { - std::string Message; - raw_string_ostream Out; - Instruction *Instr; - -public: - VectorizationReport(Instruction *I = nullptr) : Out(Message), Instr(I) { - Out << "loop not vectorized: "; - } - - template <typename A> VectorizationReport &operator<<(const A &Value) { - Out << Value; - return *this; - } - - Instruction *getInstr() { return Instr; } - - std::string &str() { return Out.str(); } - operator Twine() { return Out.str(); } - - /// \brief Emit an analysis note with the debug location from the instruction - /// in \p Message if available. Otherwise use the location of \p TheLoop. - static void emitAnalysis(VectorizationReport &Message, - const Function *TheFunction, - const Loop *TheLoop); -}; - /// InnerLoopVectorizer vectorizes loops which contain only one basic /// block to a specified vectorization factor (VF). /// This class performs the widening of scalars into vectors, or multiple @@ -557,16 +529,6 @@ static void propagateMetadata(Instruction *To, const Instruction *From) { } } -void VectorizationReport::emitAnalysis(VectorizationReport &Message, - const Function *TheFunction, - const Loop *TheLoop) { - DebugLoc DL = TheLoop->getStartLoc(); - if (Instruction *I = Message.getInstr()) - DL = I->getDebugLoc(); - emitOptimizationRemarkAnalysis(TheFunction->getContext(), DEBUG_TYPE, - *TheFunction, DL, Message.str()); -} - /// \brief Propagate known metadata from one instruction to a vector of others. static void propagateMetadata(SmallVectorImpl<Value *> &To, const Instruction *From) { for (Value *V : To) @@ -574,133 +536,6 @@ static void propagateMetadata(SmallVectorImpl<Value *> &To, const Instruction *F propagateMetadata(I, From); } -namespace { -/// \brief Drive the analysis of memory accesses in the loop -/// -/// This class is responsible for analyzing the memory accesses of a loop. It -/// collects the accesses and then its main helper the AccessAnalysis class -/// finds and categorizes the dependences in buildDependenceSets. -/// -/// For memory dependences that can be analyzed at compile time, it determines -/// whether the dependence is part of cycle inhibiting vectorization. This work -/// is delegated to the MemoryDepChecker class. -/// -/// For memory dependences that cannot be determined at compile time, it -/// generates run-time checks to prove independence. This is done by -/// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the -/// RuntimePointerCheck class. -class LoopAccessAnalysis { -public: - /// \brief Collection of parameters used from the vectorizer. - struct VectorizerParams { - /// \brief Maximum simd width. - unsigned MaxVectorWidth; - - /// \brief VF as overridden by the user. - unsigned VectorizationFactor; - /// \brief Interleave factor as overridden by the user. - unsigned VectorizationInterleave; - - /// \\brief When performing memory disambiguation checks at runtime do not - /// make more than this number of comparisons. - unsigned RuntimeMemoryCheckThreshold; - - VectorizerParams(unsigned MaxVectorWidth, - unsigned VectorizationFactor, - unsigned VectorizationInterleave, - unsigned RuntimeMemoryCheckThreshold) : - MaxVectorWidth(MaxVectorWidth), - VectorizationFactor(VectorizationFactor), - VectorizationInterleave(VectorizationInterleave), - RuntimeMemoryCheckThreshold(RuntimeMemoryCheckThreshold) {} - }; - - /// This struct holds information about the memory runtime legality check that - /// a group of pointers do not overlap. - struct RuntimePointerCheck { - RuntimePointerCheck() : Need(false) {} - - /// Reset the state of the pointer runtime information. - void reset() { - Need = false; - Pointers.clear(); - Starts.clear(); - Ends.clear(); - IsWritePtr.clear(); - DependencySetId.clear(); - AliasSetId.clear(); - } - - /// Insert a pointer and calculate the start and end SCEVs. - void insert(ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr, - unsigned DepSetId, unsigned ASId, ValueToValueMap &Strides); - - /// This flag indicates if we need to add the runtime check. - bool Need; - /// Holds the pointers that we need to check. - SmallVector<TrackingVH<Value>, 2> Pointers; - /// Holds the pointer value at the beginning of the loop. - SmallVector<const SCEV*, 2> Starts; - /// Holds the pointer value at the end of the loop. - SmallVector<const SCEV*, 2> Ends; - /// Holds the information if this pointer is used for writing to memory. - SmallVector<bool, 2> IsWritePtr; - /// Holds the id of the set of pointers that could be dependent because of a - /// shared underlying object. - SmallVector<unsigned, 2> DependencySetId; - /// Holds the id of the disjoint alias set to which this pointer belongs. - SmallVector<unsigned, 2> AliasSetId; - }; - - LoopAccessAnalysis(Function *F, Loop *L, ScalarEvolution *SE, - const DataLayout *DL, const TargetLibraryInfo *TLI, - AliasAnalysis *AA, DominatorTree *DT, - const VectorizerParams &VectParams) : - TheFunction(F), TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA), DT(DT), - NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1U), - VectParams(VectParams) {} - - /// Return true we can analyze the memory accesses in the loop and there are - /// no memory dependence cycles. Replaces symbolic strides using Strides. - bool canVectorizeMemory(ValueToValueMap &Strides); - - RuntimePointerCheck *getRuntimePointerCheck() { return &PtrRtCheck; } - - /// Return true if the block BB needs to be predicated in order for the loop - /// to be vectorized. - bool blockNeedsPredication(BasicBlock *BB); - - /// Returns true if the value V is uniform within the loop. - bool isUniform(Value *V); - - unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; } - -private: - void emitAnalysis(Report &Message) { - emitLoopAnalysis(Message, TheFunction, TheLoop); - } - - /// We need to check that all of the pointers in this list are disjoint - /// at runtime. - RuntimePointerCheck PtrRtCheck; - Function *TheFunction; - Loop *TheLoop; - ScalarEvolution *SE; - const DataLayout *DL; - const TargetLibraryInfo *TLI; - AliasAnalysis *AA; - DominatorTree *DT; - - unsigned NumLoads; - unsigned NumStores; - - unsigned MaxSafeDepDistBytes; - - /// \brief Vectorizer parameters used by the analysis. - VectorizerParams VectParams; -}; -} // end anonymous namespace - /// LoopVectorizationLegality checks if it is legal to vectorize a loop, and /// to what vectorization factor. /// This class does not look at the profitability of vectorization, only the @@ -1670,68 +1505,6 @@ struct LoopVectorize : public FunctionPass { // LoopVectorizationCostModel. //===----------------------------------------------------------------------===// -static Value *stripIntegerCast(Value *V) { - if (CastInst *CI = dyn_cast<CastInst>(V)) - if (CI->getOperand(0)->getType()->isIntegerTy()) - return CI->getOperand(0); - return V; -} - -///\brief Replaces the symbolic stride in a pointer SCEV expression by one. -/// -/// If \p OrigPtr is not null, use it to look up the stride value instead of -/// \p Ptr. -static const SCEV *replaceSymbolicStrideSCEV(ScalarEvolution *SE, - ValueToValueMap &PtrToStride, - Value *Ptr, Value *OrigPtr = nullptr) { - - const SCEV *OrigSCEV = SE->getSCEV(Ptr); - - // If there is an entry in the map return the SCEV of the pointer with the - // symbolic stride replaced by one. - ValueToValueMap::iterator SI = PtrToStride.find(OrigPtr ? OrigPtr : Ptr); - if (SI != PtrToStride.end()) { - Value *StrideVal = SI->second; - - // Strip casts. - StrideVal = stripIntegerCast(StrideVal); - - // Replace symbolic stride by one. - Value *One = ConstantInt::get(StrideVal->getType(), 1); - ValueToValueMap RewriteMap; - RewriteMap[StrideVal] = One; - - const SCEV *ByOne = - SCEVParameterRewriter::rewrite(OrigSCEV, *SE, RewriteMap, true); - DEBUG(dbgs() << "LV: Replacing SCEV: " << *OrigSCEV << " by: " << *ByOne - << "\n"); - return ByOne; - } - - // Otherwise, just return the SCEV of the original pointer. - return SE->getSCEV(Ptr); -} - -void LoopAccessAnalysis::RuntimePointerCheck::insert(ScalarEvolution *SE, - Loop *Lp, Value *Ptr, - bool WritePtr, - unsigned DepSetId, - unsigned ASId, - ValueToValueMap &Strides) { - // Get the stride replaced scev. - const SCEV *Sc = replaceSymbolicStrideSCEV(SE, Strides, Ptr); - const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc); - assert(AR && "Invalid addrec expression"); - const SCEV *Ex = SE->getBackedgeTakenCount(Lp); - const SCEV *ScEnd = AR->evaluateAtIteration(Ex, *SE); - Pointers.push_back(Ptr); - Starts.push_back(AR->getStart()); - Ends.push_back(ScEnd); - IsWritePtr.push_back(WritePtr); - DependencySetId.push_back(DepSetId); - AliasSetId.push_back(ASId); -} - Value *InnerLoopVectorizer::getBroadcastInstrs(Value *V) { // We need to place the broadcast of invariant variables outside the loop. Instruction *Instr = dyn_cast<Instruction>(V); @@ -1888,10 +1661,6 @@ int LoopVectorizationLegality::isConsecutivePtr(Value *Ptr) { return 0; } -bool LoopAccessAnalysis::isUniform(Value *V) { - return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop)); -} - bool LoopVectorizationLegality::isUniform(Value *V) { return LAA.isUniform(V); } @@ -4154,982 +3923,6 @@ void LoopVectorizationLegality::collectLoopUniforms() { } } -namespace { -/// \brief Analyses memory accesses in a loop. -/// -/// Checks whether run time pointer checks are needed and builds sets for data -/// dependence checking. -class AccessAnalysis { -public: - /// \brief Read or write access location. - typedef PointerIntPair<Value *, 1, bool> MemAccessInfo; - typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet; - - /// \brief Set of potential dependent memory accesses. - typedef EquivalenceClasses<MemAccessInfo> DepCandidates; - - AccessAnalysis(const DataLayout *Dl, AliasAnalysis *AA, DepCandidates &DA) : - DL(Dl), AST(*AA), DepCands(DA), IsRTCheckNeeded(false) {} - - /// \brief Register a load and whether it is only read from. - void addLoad(AliasAnalysis::Location &Loc, bool IsReadOnly) { - Value *Ptr = const_cast<Value*>(Loc.Ptr); - AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags); - Accesses.insert(MemAccessInfo(Ptr, false)); - if (IsReadOnly) - ReadOnlyPtr.insert(Ptr); - } - - /// \brief Register a store. - void addStore(AliasAnalysis::Location &Loc) { - Value *Ptr = const_cast<Value*>(Loc.Ptr); - AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags); - Accesses.insert(MemAccessInfo(Ptr, true)); - } - - /// \brief Check whether we can check the pointers at runtime for - /// non-intersection. - bool canCheckPtrAtRT(LoopAccessAnalysis::RuntimePointerCheck &RtCheck, - unsigned &NumComparisons, - ScalarEvolution *SE, Loop *TheLoop, - ValueToValueMap &Strides, - bool ShouldCheckStride = false); - - /// \brief Goes over all memory accesses, checks whether a RT check is needed - /// and builds sets of dependent accesses. - void buildDependenceSets() { - processMemAccesses(); - } - - bool isRTCheckNeeded() { return IsRTCheckNeeded; } - - bool isDependencyCheckNeeded() { return !CheckDeps.empty(); } - void resetDepChecks() { CheckDeps.clear(); } - - MemAccessInfoSet &getDependenciesToCheck() { return CheckDeps; } - -private: - typedef SetVector<MemAccessInfo> PtrAccessSet; - - /// \brief Go over all memory access and check whether runtime pointer checks - /// are needed /// and build sets of dependency check candidates. - void processMemAccesses(); - - /// Set of all accesses. - PtrAccessSet Accesses; - - /// Set of accesses that need a further dependence check. - MemAccessInfoSet CheckDeps; - - /// Set of pointers that are read only. - SmallPtrSet<Value*, 16> ReadOnlyPtr; - - const DataLayout *DL; - - /// An alias set tracker to partition the access set by underlying object and - //intrinsic property (such as TBAA metadata). - AliasSetTracker AST; - - /// Sets of potentially dependent accesses - members of one set share an - /// underlying pointer. The set "CheckDeps" identfies which sets really need a - /// dependence check. - DepCandidates &DepCands; - - bool IsRTCheckNeeded; -}; - -} // end anonymous namespace - -/// \brief Check whether a pointer can participate in a runtime bounds check. -static bool hasComputableBounds(ScalarEvolution *SE, ValueToValueMap &Strides, - Value *Ptr) { - const SCEV *PtrScev = replaceSymbolicStrideSCEV(SE, Strides, Ptr); - const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); - if (!AR) - return false; - - return AR->isAffine(); -} - -/// \brief Check the stride of the pointer and ensure that it does not wrap in -/// the address space. -static int isStridedPtr(ScalarEvolution *SE, const DataLayout *DL, Value *Ptr, - const Loop *Lp, ValueToValueMap &StridesMap); - -bool AccessAnalysis::canCheckPtrAtRT( - LoopAccessAnalysis::RuntimePointerCheck &RtCheck, - unsigned &NumComparisons, ScalarEvolution *SE, Loop *TheLoop, - ValueToValueMap &StridesMap, bool ShouldCheckStride) { - // Find pointers with computable bounds. We are going to use this information - // to place a runtime bound check. - bool CanDoRT = true; - - bool IsDepCheckNeeded = isDependencyCheckNeeded(); - NumComparisons = 0; - - // We assign a consecutive id to access from different alias sets. - // Accesses between different groups doesn't need to be checked. - unsigned ASId = 1; - for (auto &AS : AST) { - unsigned NumReadPtrChecks = 0; - unsigned NumWritePtrChecks = 0; - - // We assign consecutive id to access from different dependence sets. - // Accesses within the same set don't need a runtime check. - unsigned RunningDepId = 1; - DenseMap<Value *, unsigned> DepSetId; - - for (auto A : AS) { - Value *Ptr = A.getValue(); - bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true)); - MemAccessInfo Access(Ptr, IsWrite); - - if (IsWrite) - ++NumWritePtrChecks; - else - ++NumReadPtrChecks; - - if (hasComputableBounds(SE, StridesMap, Ptr) && - // When we run after a failing dependency check we have to make sure we - // don't have wrapping pointers. - (!ShouldCheckStride || - isStridedPtr(SE, DL, Ptr, TheLoop, StridesMap) == 1)) { - // The id of the dependence set. - unsigned DepId; - - if (IsDepCheckNeeded) { - Value *Leader = DepCands.getLeaderValue(Access).getPointer(); - unsigned &LeaderId = DepSetId[Leader]; - if (!LeaderId) - LeaderId = RunningDepId++; - DepId = LeaderId; - } else - // Each access has its own dependence set. - DepId = RunningDepId++; - - RtCheck.insert(SE, TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap); - - DEBUG(dbgs() << "LV: Found a runtime check ptr:" << *Ptr << '\n'); - } else { - CanDoRT = false; - } - } - - if (IsDepCheckNeeded && CanDoRT && RunningDepId == 2) - NumComparisons += 0; // Only one dependence set. - else { - NumComparisons += (NumWritePtrChecks * (NumReadPtrChecks + - NumWritePtrChecks - 1)); - } - - ++ASId; - } - - // If the pointers that we would use for the bounds comparison have different - // address spaces, assume the values aren't directly comparable, so we can't - // use them for the runtime check. We also have to assume they could - // overlap. In the future there should be metadata for whether address spaces - // are disjoint. - unsigned NumPointers = RtCheck.Pointers.size(); - for (unsigned i = 0; i < NumPointers; ++i) { - for (unsigned j = i + 1; j < NumPointers; ++j) { - // Only need to check pointers between two different dependency sets. - if (RtCheck.DependencySetId[i] == RtCheck.DependencySetId[j]) - continue; - // Only need to check pointers in the same alias set. - if (RtCheck.AliasSetId[i] != RtCheck.AliasSetId[j]) - continue; - - Value *PtrI = RtCheck.Pointers[i]; - Value *PtrJ = RtCheck.Pointers[j]; - - unsigned ASi = PtrI->getType()->getPointerAddressSpace(); - unsigned ASj = PtrJ->getType()->getPointerAddressSpace(); - if (ASi != ASj) { - DEBUG(dbgs() << "LV: Runtime check would require comparison between" - " different address spaces\n"); - return false; - } - } - } - - return CanDoRT; -} - -void AccessAnalysis::processMemAccesses() { - // We process the set twice: first we process read-write pointers, last we - // process read-only pointers. This allows us to skip dependence tests for - // read-only pointers. - - DEBUG(dbgs() << "LV: Processing memory accesses...\n"); - DEBUG(dbgs() << " AST: "; AST.dump()); - DEBUG(dbgs() << "LV: Accesses:\n"); - DEBUG({ - for (auto A : Accesses) - dbgs() << "\t" << *A.getPointer() << " (" << - (A.getInt() ? "write" : (ReadOnlyPtr.count(A.getPointer()) ? - "read-only" : "read")) << ")\n"; - }); - - // The AliasSetTracker has nicely partitioned our pointers by metadata - // compatibility and potential for underlying-object overlap. As a result, we - // only need to check for potential pointer dependencies within each alias - // set. - for (auto &AS : AST) { - // Note that both the alias-set tracker and the alias sets themselves used - // linked lists internally and so the iteration order here is deterministic - // (matching the original instruction order within each set). - - bool SetHasWrite = false; - - // Map of pointers to last access encountered. - typedef DenseMap<Value*, MemAccessInfo> UnderlyingObjToAccessMap; - UnderlyingObjToAccessMap ObjToLastAccess; - - // Set of access to check after all writes have been processed. - PtrAccessSet DeferredAccesses; - - // Iterate over each alias set twice, once to process read/write pointers, - // and then to process read-only pointers. - for (int SetIteration = 0; SetIteration < 2; ++SetIteration) { - bool UseDeferred = SetIteration > 0; - PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses; - - for (auto AV : AS) { - Value *Ptr = AV.getValue(); - - // For a single memory access in AliasSetTracker, Accesses may contain - // both read and write, and they both need to be handled for CheckDeps. - for (auto AC : S) { - if (AC.getPointer() != Ptr) - continue; - - bool IsWrite = AC.getInt(); - - // If we're using the deferred access set, then it contains only - // reads. - bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite; - if (UseDeferred && !IsReadOnlyPtr) - continue; - // Otherwise, the pointer must be in the PtrAccessSet, either as a - // read or a write. - assert(((IsReadOnlyPtr && UseDeferred) || IsWrite || - S.count(MemAccessInfo(Ptr, false))) && - "Alias-set pointer not in the access set?"); - - MemAccessInfo Access(Ptr, IsWrite); - DepCands.insert(Access); - - // Memorize read-only pointers for later processing and skip them in - // the first round (they need to be checked after we have seen all - // write pointers). Note: we also mark pointer that are not - // consecutive as "read-only" pointers (so that we check - // "a[b[i]] +="). Hence, we need the second check for "!IsWrite". - if (!UseDeferred && IsReadOnlyPtr) { - DeferredAccesses.insert(Access); - continue; - } - - // If this is a write - check other reads and writes for conflicts. If - // this is a read only check other writes for conflicts (but only if - // there is no other write to the ptr - this is an optimization to - // catch "a[i] = a[i] + " without having to do a dependence check). - if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) { - CheckDeps.insert(Access); - IsRTCheckNeeded = true; - } - - if (IsWrite) - SetHasWrite = true; - - // Create sets of pointers connected by a shared alias set and - // underlying object. - typedef SmallVector<Value *, 16> ValueVector; - ValueVector TempObjects; - GetUnderlyingObjects(Ptr, TempObjects, DL); - for (Value *UnderlyingObj : TempObjects) { - UnderlyingObjToAccessMap::iterator Prev = - ObjToLastAccess.find(UnderlyingObj); - if (Prev != ObjToLastAccess.end()) - DepCands.unionSets(Access, Prev->second); - - ObjToLastAccess[UnderlyingObj] = Access; - } - } - } - } - } -} - -namespace { -/// \brief Checks memory dependences among accesses to the same underlying -/// object to determine whether there vectorization is legal or not (and at -/// which vectorization factor). -/// -/// This class works under the assumption that we already checked that memory -/// locations with different underlying pointers are "must-not alias". -/// We use the ScalarEvolution framework to symbolically evalutate access -/// functions pairs. Since we currently don't restructure the loop we can rely -/// on the program order of memory accesses to determine their safety. -/// At the moment we will only deem accesses as safe for: -/// * A negative constant distance assuming program order. -/// -/// Safe: tmp = a[i + 1]; OR a[i + 1] = x; -/// a[i] = tmp; y = a[i]; -/// -/// The latter case is safe because later checks guarantuee that there can't -/// be a cycle through a phi node (that is, we check that "x" and "y" is not -/// the same variable: a header phi can only be an induction or a reduction, a -/// reduction can't have a memory sink, an induction can't have a memory -/// source). This is important and must not be violated (or we have to -/// resort to checking for cycles through memory). -/// -/// * A positive constant distance assuming program order that is bigger -/// than the biggest memory access. -/// -/// tmp = a[i] OR b[i] = x -/// a[i+2] = tmp y = b[i+2]; -/// -/// Safe distance: 2 x sizeof(a[0]), and 2 x sizeof(b[0]), respectively. -/// -/// * Zero distances and all accesses have the same size. -/// -class MemoryDepChecker { -public: - typedef PointerIntPair<Value *, 1, bool> MemAccessInfo; - typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet; - - MemoryDepChecker(ScalarEvolution *Se, const DataLayout *Dl, const Loop *L, - const LoopAccessAnalysis::VectorizerParams &VectParams) - : SE(Se), DL(Dl), InnermostLoop(L), AccessIdx(0), - ShouldRetryWithRuntimeCheck(false), VectParams(VectParams) {} - - /// \brief Register the location (instructions are given increasing numbers) - /// of a write access. - void addAccess(StoreInst *SI) { - Value *Ptr = SI->getPointerOperand(); - Accesses[MemAccessInfo(Ptr, true)].push_back(AccessIdx); - InstMap.push_back(SI); - ++AccessIdx; - } - - /// \brief Register the location (instructions are given increasing numbers) - /// of a write access. - void addAccess(LoadInst *LI) { - Value *Ptr = LI->getPointerOperand(); - Accesses[MemAccessInfo(Ptr, false)].push_back(AccessIdx); - InstMap.push_back(LI); - ++AccessIdx; - } - - /// \brief Check whether the dependencies between the accesses are safe. - /// - /// Only checks sets with elements in \p CheckDeps. - bool areDepsSafe(AccessAnalysis::DepCandidates &AccessSets, - MemAccessInfoSet &CheckDeps, ValueToValueMap &Strides); - - /// \brief The maximum number of bytes of a vector register we can vectorize - /// the accesses safely with. - unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; } - - /// \brief In same cases when the dependency check fails we can still - /// vectorize the loop with a dynamic array access check. - bool shouldRetryWithRuntimeCheck() { return ShouldRetryWithRuntimeCheck; } - -private: - ScalarEvolution *SE; - const DataLayout *DL; - const Loop *InnermostLoop; - - /// \brief Maps access locations (ptr, read/write) to program order. - DenseMap<MemAccessInfo, std::vector<unsigned> > Accesses; - - /// \brief Memory access instructions in program order. - SmallVector<Instruction *, 16> InstMap; - - /// \brief The program order index to be used for the next instruction. - unsigned AccessIdx; - - // We can access this many bytes in parallel safely. - unsigned MaxSafeDepDistBytes; - - /// \brief If we see a non-constant dependence distance we can still try to - /// vectorize this loop with runtime checks. - bool ShouldRetryWithRuntimeCheck; - - /// \brief Vectorizer parameters used by the analysis. - LoopAccessAnalysis::VectorizerParams VectParams; - - /// \brief Check whether there is a plausible dependence between the two - /// accesses. - /// - /// Access \p A must happen before \p B in program order. The two indices - /// identify the index into the program order map. - /// - /// This function checks whether there is a plausible dependence (or the - /// absence of such can't be proved) between the two accesses. If there is a - /// plausible dependence but the dependence distance is bigger than one - /// element access it records this distance in \p MaxSafeDepDistBytes (if this - /// distance is smaller than any other distance encountered so far). - /// Otherwise, this function returns true signaling a possible dependence. - bool isDependent(const MemAccessInfo &A, unsigned AIdx, - const MemAccessInfo &B, unsigned BIdx, - ValueToValueMap &Strides); - - /// \brief Check whether the data dependence could prevent store-load - /// forwarding. - bool couldPreventStoreLoadForward(unsigned Distance, unsigned TypeByteSize); -}; - -} // end anonymous namespace - -static bool isInBoundsGep(Value *Ptr) { - if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) - return GEP->isInBounds(); - return false; -} - -/// \brief Check whether the access through \p Ptr has a constant stride. -static int isStridedPtr(ScalarEvolution *SE, const DataLayout *DL, Value *Ptr, - const Loop *Lp, ValueToValueMap &StridesMap) { - const Type *Ty = Ptr->getType(); - assert(Ty->isPointerTy() && "Unexpected non-ptr"); - - // Make sure that the pointer does not point to aggregate types. - const PointerType *PtrTy = cast<PointerType>(Ty); - if (PtrTy->getElementType()->isAggregateType()) { - DEBUG(dbgs() << "LV: Bad stride - Not a pointer to a scalar type" << *Ptr << - "\n"); - return 0; - } - - const SCEV *PtrScev = replaceSymbolicStrideSCEV(SE, StridesMap, Ptr); - - const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); - if (!AR) { - DEBUG(dbgs() << "LV: Bad stride - Not an AddRecExpr pointer " - << *Ptr << " SCEV: " << *PtrScev << "\n"); - return 0; - } - - // The accesss function must stride over the innermost loop. - if (Lp != AR->getLoop()) { - DEBUG(dbgs() << "LV: Bad stride - Not striding over innermost loop " << - *Ptr << " SCEV: " << *PtrScev << "\n"); - } - - // The address calculation must not wrap. Otherwise, a dependence could be - // inverted. - // An inbounds getelementptr that is a AddRec with a unit stride - // cannot wrap per definition. The unit stride requirement is checked later. - // An getelementptr without an inbounds attribute and unit stride would have - // to access the pointer value "0" which is undefined behavior in address - // space 0, therefore we can also vectorize this case. - bool IsInBoundsGEP = isInBoundsGep(Ptr); - bool IsNoWrapAddRec = AR->getNoWrapFlags(SCEV::NoWrapMask); - bool IsInAddressSpaceZero = PtrTy->getAddressSpace() == 0; - if (!IsNoWrapAddRec && !IsInBoundsGEP && !IsInAddressSpaceZero) { - DEBUG(dbgs() << "LV: Bad stride - Pointer may wrap in the address space " - << *Ptr << " SCEV: " << *PtrScev << "\n"); - return 0; - } - - // Check the step is constant. - const SCEV *Step = AR->getStepRecurrence(*SE); - - // Calculate the pointer stride and check if it is consecutive. - const SCEVConstant *C = dyn_cast<SCEVConstant>(Step); - if (!C) { - DEBUG(dbgs() << "LV: Bad stride - Not a constant strided " << *Ptr << - " SCEV: " << *PtrScev << "\n"); - return 0; - } - - int64_t Size = DL->getTypeAllocSize(PtrTy->getElementType()); - const APInt &APStepVal = C->getValue()->getValue(); - - // Huge step value - give up. - if (APStepVal.getBitWidth() > 64) - return 0; - - int64_t StepVal = APStepVal.getSExtValue(); - - // Strided access. - int64_t Stride = StepVal / Size; - int64_t Rem = StepVal % Size; - if (Rem) - return 0; - - // If the SCEV could wrap but we have an inbounds gep with a unit stride we - // know we can't "wrap around the address space". In case of address space - // zero we know that this won't happen without triggering undefined behavior. - if (!IsNoWrapAddRec && (IsInBoundsGEP || IsInAddressSpaceZero) && - Stride != 1 && Stride != -1) - return 0; - - return Stride; -} - -bool MemoryDepChecker::couldPreventStoreLoadForward(unsigned Distance, - unsigned TypeByteSize) { - // If loads occur at a distance that is not a multiple of a feasible vector - // factor store-load forwarding does not take place. - // Positive dependences might cause troubles because vectorizing them might - // prevent store-load forwarding making vectorized code run a lot slower. - // a[i] = a[i-3] ^ a[i-8]; - // The stores to a[i:i+1] don't align with the stores to a[i-3:i-2] and - // hence on your typical architecture store-load forwarding does not take - // place. Vectorizing in such cases does not make sense. - // Store-load forwarding distance. - const unsigned NumCyclesForStoreLoadThroughMemory = 8*TypeByteSize; - // Maximum vector factor. - unsigned MaxVFWithoutSLForwardIssues = VectParams.MaxVectorWidth*TypeByteSize; - if(MaxSafeDepDistBytes < MaxVFWithoutSLForwardIssues) - MaxVFWithoutSLForwardIssues = MaxSafeDepDistBytes; - - for (unsigned vf = 2*TypeByteSize; vf <= MaxVFWithoutSLForwardIssues; - vf *= 2) { - if (Distance % vf && Distance / vf < NumCyclesForStoreLoadThroughMemory) { - MaxVFWithoutSLForwardIssues = (vf >>=1); - break; - } - } - - if (MaxVFWithoutSLForwardIssues< 2*TypeByteSize) { - DEBUG(dbgs() << "LV: Distance " << Distance << - " that could cause a store-load forwarding conflict\n"); - return true; - } - - if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes && - MaxVFWithoutSLForwardIssues != VectParams.MaxVectorWidth*TypeByteSize) - MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues; - return false; -} - -bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx, - const MemAccessInfo &B, unsigned BIdx, - ValueToValueMap &Strides) { - assert (AIdx < BIdx && "Must pass arguments in program order"); - - Value *APtr = A.getPointer(); - Value *BPtr = B.getPointer(); - bool AIsWrite = A.getInt(); - bool BIsWrite = B.getInt(); - - // Two reads are independent. - if (!AIsWrite && !BIsWrite) - return false; - - // We cannot check pointers in different address spaces. - if (APtr->getType()->getPointerAddressSpace() != - BPtr->getType()->getPointerAddressSpace()) - return true; - - const SCEV *AScev = replaceSymbolicStrideSCEV(SE, Strides, APtr); - const SCEV *BScev = replaceSymbolicStrideSCEV(SE, Strides, BPtr); - - int StrideAPtr = isStridedPtr(SE, DL, APtr, InnermostLoop, Strides); - int StrideBPtr = isStridedPtr(SE, DL, BPtr, InnermostLoop, Strides); - - const SCEV *Src = AScev; - const SCEV *Sink = BScev; - - // If the induction step is negative we have to invert source and sink of the - // dependence. - if (StrideAPtr < 0) { - //Src = BScev; - //Sink = AScev; - std::swap(APtr, BPtr); - std::swap(Src, Sink); - std::swap(AIsWrite, BIsWrite); - std::swap(AIdx, BIdx); - std::swap(StrideAPtr, StrideBPtr); - } - - const SCEV *Dist = SE->getMinusSCEV(Sink, Src); - - DEBUG(dbgs() << "LV: Src Scev: " << *Src << "Sink Scev: " << *Sink - << "(Induction step: " << StrideAPtr << ")\n"); - DEBUG(dbgs() << "LV: Distance for " << *InstMap[AIdx] << " to " - << *InstMap[BIdx] << ": " << *Dist << "\n"); - - // Need consecutive accesses. We don't want to vectorize - // "A[B[i]] += ..." and similar code or pointer arithmetic that could wrap in - // the address space. - if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){ - DEBUG(dbgs() << "Non-consecutive pointer access\n"); - return true; - } - - const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist); - if (!C) { - DEBUG(dbgs() << "LV: Dependence because of non-constant distance\n"); - ShouldRetryWithRuntimeCheck = true; - return true; - } - - Type *ATy = APtr->getType()->getPointerElementType(); - Type *BTy = BPtr->getType()->getPointerElementType(); - unsigned TypeByteSize = DL->getTypeAllocSize(ATy); - - // Negative distances are not plausible dependencies. - const APInt &Val = C->getValue()->getValue(); - if (Val.isNegative()) { - bool IsTrueDataDependence = (AIsWrite && !BIsWrite); - if (IsTrueDataDependence && - (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) || - ATy != BTy)) - return true; - - DEBUG(dbgs() << "LV: Dependence is negative: NoDep\n"); - return false; - } - - // Write to the same location with the same size. - // Could be improved to assert type sizes are the same (i32 == float, etc). - if (Val == 0) { - if (ATy == BTy) - return false; - DEBUG(dbgs() << "LV: Zero dependence difference but different types\n"); - return true; - } - - assert(Val.isStrictlyPositive() && "Expect a positive value"); - - // Positive distance bigger than max vectorization factor. - if (ATy != BTy) { - DEBUG(dbgs() << - "LV: ReadWrite-Write positive dependency with different types\n"); - return false; - } - - unsigned Distance = (unsigned) Val.getZExtValue(); - - // Bail out early if passed-in parameters make vectorization not feasible. - unsigned ForcedFactor = (VectParams.VectorizationFactor ? - VectParams.VectorizationFactor : 1); - unsigned ForcedUnroll = (VectParams.VectorizationInterleave ? - VectParams.VectorizationInterleave : 1); - - // The distance must be bigger than the size needed for a vectorized version - // of the operation and the size of the vectorized operation must not be - // bigger than the currrent maximum size. - if (Distance < 2*TypeByteSize || - 2*TypeByteSize > MaxSafeDepDistBytes || - Distance < TypeByteSize * ForcedUnroll * ForcedFactor) { - DEBUG(dbgs() << "LV: Failure because of Positive distance " - << Val.getSExtValue() << '\n'); - return true; - } - - MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ? - Distance : MaxSafeDepDistBytes; - - bool IsTrueDataDependence = (!AIsWrite && BIsWrite); - if (IsTrueDataDependence && - couldPreventStoreLoadForward(Distance, TypeByteSize)) - return true; - - DEBUG(dbgs() << "LV: Positive distance " << Val.getSExtValue() << - " with max VF = " << MaxSafeDepDistBytes / TypeByteSize << '\n'); - - return false; -} - -bool MemoryDepChecker::areDepsSafe(AccessAnalysis::DepCandidates &AccessSets, - MemAccessInfoSet &CheckDeps, - ValueToValueMap &Strides) { - - MaxSafeDepDistBytes = -1U; - while (!CheckDeps.empty()) { - MemAccessInfo CurAccess = *CheckDeps.begin(); - - // Get the relevant memory access set. - EquivalenceClasses<MemAccessInfo>::iterator I = - AccessSets.findValue(AccessSets.getLeaderValue(CurAccess)); - - // Check accesses within this set. - EquivalenceClasses<MemAccessInfo>::member_iterator AI, AE; - AI = AccessSets.member_begin(I), AE = AccessSets.member_end(); - - // Check every access pair. - while (AI != AE) { - CheckDeps.erase(*AI); - EquivalenceClasses<MemAccessInfo>::member_iterator OI = std::next(AI); - while (OI != AE) { - // Check every accessing instruction pair in program order. - for (std::vector<unsigned>::iterator I1 = Accesses[*AI].begin(), - I1E = Accesses[*AI].end(); I1 != I1E; ++I1) - for (std::vector<unsigned>::iterator I2 = Accesses[*OI].begin(), - I2E = Accesses[*OI].end(); I2 != I2E; ++I2) { - if (*I1 < *I2 && isDependent(*AI, *I1, *OI, *I2, Strides)) - return false; - if (*I2 < *I1 && isDependent(*OI, *I2, *AI, *I1, Strides)) - return false; - } - ++OI; - } - AI++; - } - } - return true; -} - -bool LoopAccessAnalysis::canVectorizeMemory(ValueToValueMap &Strides) { - - typedef SmallVector<Value*, 16> ValueVector; - typedef SmallPtrSet<Value*, 16> ValueSet; - - // Holds the Load and Store *instructions*. - ValueVector Loads; - ValueVector Stores; - - // Holds all the different accesses in the loop. - unsigned NumReads = 0; - unsigned NumReadWrites = 0; - - PtrRtCheck.Pointers.clear(); - PtrRtCheck.Need = false; - - const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel(); - MemoryDepChecker DepChecker(SE, DL, TheLoop, VectParams); - - // For each block. - for (Loop::block_iterator bb = TheLoop->block_begin(), - be = TheLoop->block_end(); bb != be; ++bb) { - - // Scan the BB and collect legal loads and stores. - for (BasicBlock::iterator it = (*bb)->begin(), e = (*bb)->end(); it != e; - ++it) { - - // If this is a load, save it. If this instruction can read from memory - // but is not a load, then we quit. Notice that we don't handle function - // calls that read or write. - if (it->mayReadFromMemory()) { - // Many math library functions read the rounding mode. We will only - // vectorize a loop if it contains known function calls that don't set - // the flag. Therefore, it is safe to ignore this read from memory. - CallInst *Call = dyn_cast<CallInst>(it); - if (Call && getIntrinsicIDForCall(Call, TLI)) - continue; - - LoadInst *Ld = dyn_cast<LoadInst>(it); - if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) { - emitAnalysis(VectorizationReport(Ld) - << "read with atomic ordering or volatile read"); - DEBUG(dbgs() << "LV: Found a non-simple load.\n"); - return false; - } - NumLoads++; - Loads.push_back(Ld); - DepChecker.addAccess(Ld); - continue; - } - - // Save 'store' instructions. Abort if other instructions write to memory. - if (it->mayWriteToMemory()) { - StoreInst *St = dyn_cast<StoreInst>(it); - if (!St) { - emitAnalysis(VectorizationReport(it) << - "instruction cannot be vectorized"); - return false; - } - if (!St->isSimple() && !IsAnnotatedParallel) { - emitAnalysis(VectorizationReport(St) - << "write with atomic ordering or volatile write"); - DEBUG(dbgs() << "LV: Found a non-simple store.\n"); - return false; - } - NumStores++; - Stores.push_back(St); - DepChecker.addAccess(St); - } - } // Next instr. - } // Next block. - - // Now we have two lists that hold the loads and the stores. - // Next, we find the pointers that they use. - - // Check if we see any stores. If there are no stores, then we don't - // care if the pointers are *restrict*. - if (!Stores.size()) { - DEBUG(dbgs() << "LV: Found a read-only loop!\n"); - return true; - } - - AccessAnalysis::DepCandidates DependentAccesses; - AccessAnalysis Accesses(DL, AA, DependentAccesses); - - // Holds the analyzed pointers. We don't want to call GetUnderlyingObjects - // multiple times on the same object. If the ptr is accessed twice, once - // for read and once for write, it will only appear once (on the write - // list). This is okay, since we are going to check for conflicts between - // writes and between reads and writes, but not between reads and reads. - ValueSet Seen; - - ValueVector::iterator I, IE; - for (I = Stores.begin(), IE = Stores.end(); I != IE; ++I) { - StoreInst *ST = cast<StoreInst>(*I); - Value* Ptr = ST->getPointerOperand(); - - if (isUniform(Ptr)) { - emitAnalysis( - VectorizationReport(ST) - << "write to a loop invariant address could not be vectorized"); - DEBUG(dbgs() << "LV: We don't allow storing to uniform addresses\n"); - return false; - } - - // If we did *not* see this pointer before, insert it to the read-write - // list. At this phase it is only a 'write' list. - if (Seen.insert(Ptr).second) { - ++NumReadWrites; - - AliasAnalysis::Location Loc = AA->getLocation(ST); - // The TBAA metadata could have a control dependency on the predication - // condition, so we cannot rely on it when determining whether or not we - // need runtime pointer checks. - if (blockNeedsPredication(ST->getParent())) - Loc.AATags.TBAA = nullptr; - - Accesses.addStore(Loc); - } - } - - if (IsAnnotatedParallel) { - DEBUG(dbgs() - << "LV: A loop annotated parallel, ignore memory dependency " - << "checks.\n"); - return true; - } - - for (I = Loads.begin(), IE = Loads.end(); I != IE; ++I) { - LoadInst *LD = cast<LoadInst>(*I); - Value* Ptr = LD->getPointerOperand(); - // If we did *not* see this pointer before, insert it to the - // read list. If we *did* see it before, then it is already in - // the read-write list. This allows us to vectorize expressions - // such as A[i] += x; Because the address of A[i] is a read-write - // pointer. This only works if the index of A[i] is consecutive. - // If the address of i is unknown (for example A[B[i]]) then we may - // read a few words, modify, and write a few words, and some of the - // words may be written to the same address. - bool IsReadOnlyPtr = false; - if (Seen.insert(Ptr).second || - !isStridedPtr(SE, DL, Ptr, TheLoop, Strides)) { - ++NumReads; - IsReadOnlyPtr = true; - } - - AliasAnalysis::Location Loc = AA->getLocation(LD); - // The TBAA metadata could have a control dependency on the predication - // condition, so we cannot rely on it when determining whether or not we - // need runtime pointer checks. - if (blockNeedsPredication(LD->getParent())) - Loc.AATags.TBAA = nullptr; - - Accesses.addLoad(Loc, IsReadOnlyPtr); - } - - // If we write (or read-write) to a single destination and there are no - // other reads in this loop then is it safe to vectorize. - if (NumReadWrites == 1 && NumReads == 0) { - DEBUG(dbgs() << "LV: Found a write-only loop!\n"); - return true; - } - - // Build dependence sets and check whether we need a runtime pointer bounds - // check. - Accesses.buildDependenceSets(); - bool NeedRTCheck = Accesses.isRTCheckNeeded(); - - // Find pointers with computable bounds. We are going to use this information - // to place a runtime bound check. - unsigned NumComparisons = 0; - bool CanDoRT = false; - if (NeedRTCheck) - CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop, - Strides); - - DEBUG(dbgs() << "LV: We need to do " << NumComparisons << - " pointer comparisons.\n"); - - // If we only have one set of dependences to check pointers among we don't - // need a runtime check. - if (NumComparisons == 0 && NeedRTCheck) - NeedRTCheck = false; - - // Check that we did not collect too many pointers or found an unsizeable - // pointer. - if (!CanDoRT || NumComparisons > VectParams.RuntimeMemoryCheckThreshold) { - PtrRtCheck.reset(); - CanDoRT = false; - } - - if (CanDoRT) { - DEBUG(dbgs() << "LV: We can perform a memory runtime check if needed.\n"); - } - - if (NeedRTCheck && !CanDoRT) { - emitAnalysis(VectorizationReport() << "cannot identify array bounds"); - DEBUG(dbgs() << "LV: We can't vectorize because we can't find " << - "the array bounds.\n"); - PtrRtCheck.reset(); - return false; - } - - PtrRtCheck.Need = NeedRTCheck; - - bool CanVecMem = true; - if (Accesses.isDependencyCheckNeeded()) { - DEBUG(dbgs() << "LV: Checking memory dependencies\n"); - CanVecMem = DepChecker.areDepsSafe( - DependentAccesses, Accesses.getDependenciesToCheck(), Strides); - MaxSafeDepDistBytes = DepChecker.getMaxSafeDepDistBytes(); - - if (!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()) { - DEBUG(dbgs() << "LV: Retrying with memory checks\n"); - NeedRTCheck = true; - - // Clear the dependency checks. We assume they are not needed. - Accesses.resetDepChecks(); - - PtrRtCheck.reset(); - PtrRtCheck.Need = true; - - CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, - TheLoop, Strides, true); - // Check that we did not collect too many pointers or found an unsizeable - // pointer. - if (!CanDoRT || NumComparisons > VectParams.RuntimeMemoryCheckThreshold) { - if (!CanDoRT && NumComparisons > 0) - emitAnalysis(VectorizationReport() - << "cannot check memory dependencies at runtime"); - else - emitAnalysis(VectorizationReport() - << NumComparisons << " exceeds limit of " - << VectParams.RuntimeMemoryCheckThreshold - << " dependent memory operations checked at runtime"); - DEBUG(dbgs() << "LV: Can't vectorize with memory checks\n"); - PtrRtCheck.reset(); - return false; - } - - CanVecMem = true; - } - } - - if (!CanVecMem) - emitAnalysis(VectorizationReport() << - "unsafe dependent memory operations in loop"); - - DEBUG(dbgs() << "LV: We" << (NeedRTCheck ? "" : " don't") << - " need a runtime memory check.\n"); - - return CanVecMem; -} - bool LoopVectorizationLegality::canVectorizeMemory() { return LAA.canVectorizeMemory(Strides); } @@ -5474,14 +4267,6 @@ bool LoopVectorizationLegality::isInductionVariable(const Value *V) { return Inductions.count(PN); } -bool LoopAccessAnalysis::blockNeedsPredication(BasicBlock *BB) { - assert(TheLoop->contains(BB) && "Unknown block used"); - - // Blocks that do not dominate the latch need predication. - BasicBlock* Latch = TheLoop->getLoopLatch(); - return !DT->dominates(BB, Latch); -} - bool LoopVectorizationLegality::blockNeedsPredication(BasicBlock *BB) { return LAA.blockNeedsPredication(BB); } |
