| //===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // The implementation for the loop memory dependence that was originally |
| // developed for the loop vectorizer. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/LoopAccessAnalysis.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/ScalarEvolutionExpander.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/IR/DiagnosticInfo.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/IRBuilder.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Utils/VectorUtils.h" |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "loop-accesses" |
| |
| static cl::opt<unsigned, true> |
| VectorizationFactor("force-vector-width", cl::Hidden, |
| cl::desc("Sets the SIMD width. Zero is autoselect."), |
| cl::location(VectorizerParams::VectorizationFactor)); |
| unsigned VectorizerParams::VectorizationFactor; |
| |
| static cl::opt<unsigned, true> |
| VectorizationInterleave("force-vector-interleave", cl::Hidden, |
| cl::desc("Sets the vectorization interleave count. " |
| "Zero is autoselect."), |
| cl::location( |
| VectorizerParams::VectorizationInterleave)); |
| unsigned VectorizerParams::VectorizationInterleave; |
| |
| static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold( |
| "runtime-memory-check-threshold", cl::Hidden, |
| cl::desc("When performing memory disambiguation checks at runtime do not " |
| "generate more than this number of comparisons (default = 8)."), |
| cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8)); |
| unsigned VectorizerParams::RuntimeMemoryCheckThreshold; |
| |
| /// Maximum SIMD width. |
| const unsigned VectorizerParams::MaxVectorWidth = 64; |
| |
| /// \brief We collect interesting dependences up to this threshold. |
| static cl::opt<unsigned> MaxInterestingDependence( |
| "max-interesting-dependences", cl::Hidden, |
| cl::desc("Maximum number of interesting dependences collected by " |
| "loop-access analysis (default = 100)"), |
| cl::init(100)); |
| |
| bool VectorizerParams::isInterleaveForced() { |
| return ::VectorizationInterleave.getNumOccurrences() > 0; |
| } |
| |
| void LoopAccessReport::emitAnalysis(const LoopAccessReport &Message, |
| const Function *TheFunction, |
| const Loop *TheLoop, |
| const char *PassName) { |
| DebugLoc DL = TheLoop->getStartLoc(); |
| if (const Instruction *I = Message.getInstr()) |
| DL = I->getDebugLoc(); |
| emitOptimizationRemarkAnalysis(TheFunction->getContext(), PassName, |
| *TheFunction, DL, Message.str()); |
| } |
| |
| Value *llvm::stripIntegerCast(Value *V) { |
| if (CastInst *CI = dyn_cast<CastInst>(V)) |
| if (CI->getOperand(0)->getType()->isIntegerTy()) |
| return CI->getOperand(0); |
| return V; |
| } |
| |
| const SCEV *llvm::replaceSymbolicStrideSCEV(ScalarEvolution *SE, |
| const ValueToValueMap &PtrToStride, |
| Value *Ptr, Value *OrigPtr) { |
| |
| 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::const_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() << "LAA: Replacing SCEV: " << *OrigSCEV << " by: " << *ByOne |
| << "\n"); |
| return ByOne; |
| } |
| |
| // Otherwise, just return the SCEV of the original pointer. |
| return SE->getSCEV(Ptr); |
| } |
| |
| void LoopAccessInfo::RuntimePointerCheck::insert( |
| ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr, unsigned DepSetId, |
| unsigned ASId, const 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); |
| } |
| |
| bool LoopAccessInfo::RuntimePointerCheck::needsChecking( |
| unsigned I, unsigned J, const SmallVectorImpl<int> *PtrPartition) const { |
| // No need to check if two readonly pointers intersect. |
| if (!IsWritePtr[I] && !IsWritePtr[J]) |
| return false; |
| |
| // Only need to check pointers between two different dependency sets. |
| if (DependencySetId[I] == DependencySetId[J]) |
| return false; |
| |
| // Only need to check pointers in the same alias set. |
| if (AliasSetId[I] != AliasSetId[J]) |
| return false; |
| |
| // If PtrPartition is set omit checks between pointers of the same partition. |
| // Partition number -1 means that the pointer is used in multiple partitions. |
| // In this case we can't omit the check. |
| if (PtrPartition && (*PtrPartition)[I] != -1 && |
| (*PtrPartition)[I] == (*PtrPartition)[J]) |
| return false; |
| |
| return true; |
| } |
| |
| void LoopAccessInfo::RuntimePointerCheck::print( |
| raw_ostream &OS, unsigned Depth, |
| const SmallVectorImpl<int> *PtrPartition) const { |
| unsigned NumPointers = Pointers.size(); |
| if (NumPointers == 0) |
| return; |
| |
| OS.indent(Depth) << "Run-time memory checks:\n"; |
| unsigned N = 0; |
| for (unsigned I = 0; I < NumPointers; ++I) |
| for (unsigned J = I + 1; J < NumPointers; ++J) |
| if (needsChecking(I, J, PtrPartition)) { |
| OS.indent(Depth) << N++ << ":\n"; |
| OS.indent(Depth + 2) << *Pointers[I]; |
| if (PtrPartition) |
| OS << " (Partition: " << (*PtrPartition)[I] << ")"; |
| OS << "\n"; |
| OS.indent(Depth + 2) << *Pointers[J]; |
| if (PtrPartition) |
| OS << " (Partition: " << (*PtrPartition)[J] << ")"; |
| OS << "\n"; |
| } |
| } |
| |
| 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; |
| |
| AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA, |
| MemoryDepChecker::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(LoopAccessInfo::RuntimePointerCheck &RtCheck, |
| unsigned &NumComparisons, ScalarEvolution *SE, |
| Loop *TheLoop, const 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; |
| |
| const DataLayout &DL; |
| |
| /// Set of accesses that need a further dependence check. |
| MemAccessInfoSet CheckDeps; |
| |
| /// Set of pointers that are read only. |
| SmallPtrSet<Value*, 16> ReadOnlyPtr; |
| |
| /// 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. |
| MemoryDepChecker::DepCandidates &DepCands; |
| |
| bool IsRTCheckNeeded; |
| }; |
| |
| } // end anonymous namespace |
| |
| /// \brief Check whether a pointer can participate in a runtime bounds check. |
| static bool hasComputableBounds(ScalarEvolution *SE, |
| const 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, Value *Ptr, const Loop *Lp, |
| const ValueToValueMap &StridesMap); |
| |
| bool AccessAnalysis::canCheckPtrAtRT( |
| LoopAccessInfo::RuntimePointerCheck &RtCheck, unsigned &NumComparisons, |
| ScalarEvolution *SE, Loop *TheLoop, const 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, 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() << "LAA: 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() << "LAA: 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() << "LAA: Processing memory accesses...\n"); |
| DEBUG(dbgs() << " AST: "; AST.dump()); |
| DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\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; |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| 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, Value *Ptr, const Loop *Lp, |
| const 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() << "LAA: 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() << "LAA: 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() << "LAA: 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() << "LAA: 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() << "LAA: Bad stride - Not a constant strided " << *Ptr << |
| " SCEV: " << *PtrScev << "\n"); |
| return 0; |
| } |
| |
| auto &DL = Lp->getHeader()->getModule()->getDataLayout(); |
| 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::Dependence::isSafeForVectorization(DepType Type) { |
| switch (Type) { |
| case NoDep: |
| case Forward: |
| case BackwardVectorizable: |
| return true; |
| |
| case Unknown: |
| case ForwardButPreventsForwarding: |
| case Backward: |
| case BackwardVectorizableButPreventsForwarding: |
| return false; |
| } |
| llvm_unreachable("unexpected DepType!"); |
| } |
| |
| bool MemoryDepChecker::Dependence::isInterestingDependence(DepType Type) { |
| switch (Type) { |
| case NoDep: |
| case Forward: |
| return false; |
| |
| case BackwardVectorizable: |
| case Unknown: |
| case ForwardButPreventsForwarding: |
| case Backward: |
| case BackwardVectorizableButPreventsForwarding: |
| return true; |
| } |
| llvm_unreachable("unexpected DepType!"); |
| } |
| |
| bool MemoryDepChecker::Dependence::isPossiblyBackward() const { |
| switch (Type) { |
| case NoDep: |
| case Forward: |
| case ForwardButPreventsForwarding: |
| return false; |
| |
| case Unknown: |
| case BackwardVectorizable: |
| case Backward: |
| case BackwardVectorizableButPreventsForwarding: |
| return true; |
| } |
| llvm_unreachable("unexpected DepType!"); |
| } |
| |
| 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 = |
| VectorizerParams::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() << "LAA: Distance " << Distance << |
| " that could cause a store-load forwarding conflict\n"); |
| return true; |
| } |
| |
| if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes && |
| MaxVFWithoutSLForwardIssues != |
| VectorizerParams::MaxVectorWidth * TypeByteSize) |
| MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues; |
| return false; |
| } |
| |
| MemoryDepChecker::Dependence::DepType |
| MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx, |
| const MemAccessInfo &B, unsigned BIdx, |
| const 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 Dependence::NoDep; |
| |
| // We cannot check pointers in different address spaces. |
| if (APtr->getType()->getPointerAddressSpace() != |
| BPtr->getType()->getPointerAddressSpace()) |
| return Dependence::Unknown; |
| |
| const SCEV *AScev = replaceSymbolicStrideSCEV(SE, Strides, APtr); |
| const SCEV *BScev = replaceSymbolicStrideSCEV(SE, Strides, BPtr); |
| |
| int StrideAPtr = isStridedPtr(SE, APtr, InnermostLoop, Strides); |
| int StrideBPtr = isStridedPtr(SE, 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() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sink |
| << "(Induction step: " << StrideAPtr << ")\n"); |
| DEBUG(dbgs() << "LAA: 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 Dependence::Unknown; |
| } |
| |
| const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist); |
| if (!C) { |
| DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n"); |
| ShouldRetryWithRuntimeCheck = true; |
| return Dependence::Unknown; |
| } |
| |
| Type *ATy = APtr->getType()->getPointerElementType(); |
| Type *BTy = BPtr->getType()->getPointerElementType(); |
| auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout(); |
| 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 Dependence::ForwardButPreventsForwarding; |
| |
| DEBUG(dbgs() << "LAA: Dependence is negative: NoDep\n"); |
| return Dependence::Forward; |
| } |
| |
| // 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 Dependence::NoDep; |
| DEBUG(dbgs() << "LAA: Zero dependence difference but different types\n"); |
| return Dependence::Unknown; |
| } |
| |
| assert(Val.isStrictlyPositive() && "Expect a positive value"); |
| |
| if (ATy != BTy) { |
| DEBUG(dbgs() << |
| "LAA: ReadWrite-Write positive dependency with different types\n"); |
| return Dependence::Unknown; |
| } |
| |
| unsigned Distance = (unsigned) Val.getZExtValue(); |
| |
| // Bail out early if passed-in parameters make vectorization not feasible. |
| unsigned ForcedFactor = (VectorizerParams::VectorizationFactor ? |
| VectorizerParams::VectorizationFactor : 1); |
| unsigned ForcedUnroll = (VectorizerParams::VectorizationInterleave ? |
| VectorizerParams::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() << "LAA: Failure because of Positive distance " |
| << Val.getSExtValue() << '\n'); |
| return Dependence::Backward; |
| } |
| |
| // Positive distance bigger than max vectorization factor. |
| MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ? |
| Distance : MaxSafeDepDistBytes; |
| |
| bool IsTrueDataDependence = (!AIsWrite && BIsWrite); |
| if (IsTrueDataDependence && |
| couldPreventStoreLoadForward(Distance, TypeByteSize)) |
| return Dependence::BackwardVectorizableButPreventsForwarding; |
| |
| DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue() << |
| " with max VF = " << MaxSafeDepDistBytes / TypeByteSize << '\n'); |
| |
| return Dependence::BackwardVectorizable; |
| } |
| |
| bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets, |
| MemAccessInfoSet &CheckDeps, |
| const 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) { |
| auto A = std::make_pair(&*AI, *I1); |
| auto B = std::make_pair(&*OI, *I2); |
| |
| assert(*I1 != *I2); |
| if (*I1 > *I2) |
| std::swap(A, B); |
| |
| Dependence::DepType Type = |
| isDependent(*A.first, A.second, *B.first, B.second, Strides); |
| SafeForVectorization &= Dependence::isSafeForVectorization(Type); |
| |
| // Gather dependences unless we accumulated MaxInterestingDependence |
| // dependences. In that case return as soon as we find the first |
| // unsafe dependence. This puts a limit on this quadratic |
| // algorithm. |
| if (RecordInterestingDependences) { |
| if (Dependence::isInterestingDependence(Type)) |
| InterestingDependences.push_back( |
| Dependence(A.second, B.second, Type)); |
| |
| if (InterestingDependences.size() >= MaxInterestingDependence) { |
| RecordInterestingDependences = false; |
| InterestingDependences.clear(); |
| DEBUG(dbgs() << "Too many dependences, stopped recording\n"); |
| } |
| } |
| if (!RecordInterestingDependences && !SafeForVectorization) |
| return false; |
| } |
| ++OI; |
| } |
| AI++; |
| } |
| } |
| |
| DEBUG(dbgs() << "Total Interesting Dependences: " |
| << InterestingDependences.size() << "\n"); |
| return SafeForVectorization; |
| } |
| |
| SmallVector<Instruction *, 4> |
| MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const { |
| MemAccessInfo Access(Ptr, isWrite); |
| auto &IndexVector = Accesses.find(Access)->second; |
| |
| SmallVector<Instruction *, 4> Insts; |
| std::transform(IndexVector.begin(), IndexVector.end(), |
| std::back_inserter(Insts), |
| [&](unsigned Idx) { return this->InstMap[Idx]; }); |
| return Insts; |
| } |
| |
| const char *MemoryDepChecker::Dependence::DepName[] = { |
| "NoDep", "Unknown", "Forward", "ForwardButPreventsForwarding", "Backward", |
| "BackwardVectorizable", "BackwardVectorizableButPreventsForwarding"}; |
| |
| void MemoryDepChecker::Dependence::print( |
| raw_ostream &OS, unsigned Depth, |
| const SmallVectorImpl<Instruction *> &Instrs) const { |
| OS.indent(Depth) << DepName[Type] << ":\n"; |
| OS.indent(Depth + 2) << *Instrs[Source] << " -> \n"; |
| OS.indent(Depth + 2) << *Instrs[Destination] << "\n"; |
| } |
| |
| bool LoopAccessInfo::canAnalyzeLoop() { |
| // We can only analyze innermost loops. |
| if (!TheLoop->empty()) { |
| emitAnalysis(LoopAccessReport() << "loop is not the innermost loop"); |
| return false; |
| } |
| |
| // We must have a single backedge. |
| if (TheLoop->getNumBackEdges() != 1) { |
| emitAnalysis( |
| LoopAccessReport() << |
| "loop control flow is not understood by analyzer"); |
| return false; |
| } |
| |
| // We must have a single exiting block. |
| if (!TheLoop->getExitingBlock()) { |
| emitAnalysis( |
| LoopAccessReport() << |
| "loop control flow is not understood by analyzer"); |
| return false; |
| } |
| |
| // We only handle bottom-tested loops, i.e. loop in which the condition is |
| // checked at the end of each iteration. With that we can assume that all |
| // instructions in the loop are executed the same number of times. |
| if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) { |
| emitAnalysis( |
| LoopAccessReport() << |
| "loop control flow is not understood by analyzer"); |
| return false; |
| } |
| |
| // We need to have a loop header. |
| DEBUG(dbgs() << "LAA: Found a loop: " << |
| TheLoop->getHeader()->getName() << '\n'); |
| |
| // ScalarEvolution needs to be able to find the exit count. |
| const SCEV *ExitCount = SE->getBackedgeTakenCount(TheLoop); |
| if (ExitCount == SE->getCouldNotCompute()) { |
| emitAnalysis(LoopAccessReport() << |
| "could not determine number of loop iterations"); |
| DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n"); |
| return false; |
| } |
| |
| return true; |
| } |
| |
| void LoopAccessInfo::analyzeLoop(const 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(); |
| |
| // 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; |
| |
| // If the function has an explicit vectorized counterpart, we can safely |
| // assume that it can be vectorized. |
| if (Call && !Call->isNoBuiltin() && Call->getCalledFunction() && |
| TLI->isFunctionVectorizable(Call->getCalledFunction()->getName())) |
| continue; |
| |
| LoadInst *Ld = dyn_cast<LoadInst>(it); |
| if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) { |
| emitAnalysis(LoopAccessReport(Ld) |
| << "read with atomic ordering or volatile read"); |
| DEBUG(dbgs() << "LAA: Found a non-simple load.\n"); |
| CanVecMem = false; |
| return; |
| } |
| 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(LoopAccessReport(it) << |
| "instruction cannot be vectorized"); |
| CanVecMem = false; |
| return; |
| } |
| if (!St->isSimple() && !IsAnnotatedParallel) { |
| emitAnalysis(LoopAccessReport(St) |
| << "write with atomic ordering or volatile write"); |
| DEBUG(dbgs() << "LAA: Found a non-simple store.\n"); |
| CanVecMem = false; |
| return; |
| } |
| 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() << "LAA: Found a read-only loop!\n"); |
| CanVecMem = true; |
| return; |
| } |
| |
| MemoryDepChecker::DepCandidates DependentAccesses; |
| AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(), |
| 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( |
| LoopAccessReport(ST) |
| << "write to a loop invariant address could not be vectorized"); |
| DEBUG(dbgs() << "LAA: We don't allow storing to uniform addresses\n"); |
| CanVecMem = false; |
| return; |
| } |
| |
| // 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(), TheLoop, DT)) |
| Loc.AATags.TBAA = nullptr; |
| |
| Accesses.addStore(Loc); |
| } |
| } |
| |
| if (IsAnnotatedParallel) { |
| DEBUG(dbgs() |
| << "LAA: A loop annotated parallel, ignore memory dependency " |
| << "checks.\n"); |
| CanVecMem = true; |
| return; |
| } |
| |
| 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, 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(), TheLoop, DT)) |
| 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() << "LAA: Found a write-only loop!\n"); |
| CanVecMem = true; |
| return; |
| } |
| |
| // 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. |
| bool CanDoRT = false; |
| if (NeedRTCheck) |
| CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop, |
| Strides); |
| |
| DEBUG(dbgs() << "LAA: 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 found the bounds for the pointer. |
| if (CanDoRT) |
| DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n"); |
| else if (NeedRTCheck) { |
| emitAnalysis(LoopAccessReport() << "cannot identify array bounds"); |
| DEBUG(dbgs() << "LAA: We can't vectorize because we can't find " << |
| "the array bounds.\n"); |
| PtrRtCheck.reset(); |
| CanVecMem = false; |
| return; |
| } |
| |
| PtrRtCheck.Need = NeedRTCheck; |
| |
| CanVecMem = true; |
| if (Accesses.isDependencyCheckNeeded()) { |
| DEBUG(dbgs() << "LAA: Checking memory dependencies\n"); |
| CanVecMem = DepChecker.areDepsSafe( |
| DependentAccesses, Accesses.getDependenciesToCheck(), Strides); |
| MaxSafeDepDistBytes = DepChecker.getMaxSafeDepDistBytes(); |
| |
| if (!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()) { |
| DEBUG(dbgs() << "LAA: 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 found the bounds for the pointer. |
| if (!CanDoRT && NumComparisons > 0) { |
| emitAnalysis(LoopAccessReport() |
| << "cannot check memory dependencies at runtime"); |
| DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n"); |
| PtrRtCheck.reset(); |
| CanVecMem = false; |
| return; |
| } |
| |
| CanVecMem = true; |
| } |
| } |
| |
| if (CanVecMem) |
| DEBUG(dbgs() << "LAA: No unsafe dependent memory operations in loop. We" |
| << (NeedRTCheck ? "" : " don't") |
| << " need a runtime memory check.\n"); |
| else { |
| emitAnalysis(LoopAccessReport() << |
| "unsafe dependent memory operations in loop"); |
| DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n"); |
| } |
| } |
| |
| bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop, |
| DominatorTree *DT) { |
| 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); |
| } |
| |
| void LoopAccessInfo::emitAnalysis(LoopAccessReport &Message) { |
| assert(!Report && "Multiple reports generated"); |
| Report = Message; |
| } |
| |
| bool LoopAccessInfo::isUniform(Value *V) const { |
| return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop)); |
| } |
| |
| // FIXME: this function is currently a duplicate of the one in |
| // LoopVectorize.cpp. |
| static Instruction *getFirstInst(Instruction *FirstInst, Value *V, |
| Instruction *Loc) { |
| if (FirstInst) |
| return FirstInst; |
| if (Instruction *I = dyn_cast<Instruction>(V)) |
| return I->getParent() == Loc->getParent() ? I : nullptr; |
| return nullptr; |
| } |
| |
| std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeCheck( |
| Instruction *Loc, const SmallVectorImpl<int> *PtrPartition) const { |
| Instruction *tnullptr = nullptr; |
| if (!PtrRtCheck.Need) |
| return std::pair<Instruction *, Instruction *>(tnullptr, tnullptr); |
| |
| unsigned NumPointers = PtrRtCheck.Pointers.size(); |
| SmallVector<TrackingVH<Value> , 2> Starts; |
| SmallVector<TrackingVH<Value> , 2> Ends; |
| |
| LLVMContext &Ctx = Loc->getContext(); |
| SCEVExpander Exp(*SE, DL, "induction"); |
| Instruction *FirstInst = nullptr; |
| |
| for (unsigned i = 0; i < NumPointers; ++i) { |
| Value *Ptr = PtrRtCheck.Pointers[i]; |
| const SCEV *Sc = SE->getSCEV(Ptr); |
| |
| if (SE->isLoopInvariant(Sc, TheLoop)) { |
| DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" << |
| *Ptr <<"\n"); |
| Starts.push_back(Ptr); |
| Ends.push_back(Ptr); |
| } else { |
| DEBUG(dbgs() << "LAA: Adding RT check for range:" << *Ptr << '\n'); |
| unsigned AS = Ptr->getType()->getPointerAddressSpace(); |
| |
| // Use this type for pointer arithmetic. |
| Type *PtrArithTy = Type::getInt8PtrTy(Ctx, AS); |
| |
| Value *Start = Exp.expandCodeFor(PtrRtCheck.Starts[i], PtrArithTy, Loc); |
| Value *End = Exp.expandCodeFor(PtrRtCheck.Ends[i], PtrArithTy, Loc); |
| Starts.push_back(Start); |
| Ends.push_back(End); |
| } |
| } |
| |
| IRBuilder<> ChkBuilder(Loc); |
| // Our instructions might fold to a constant. |
| Value *MemoryRuntimeCheck = nullptr; |
| for (unsigned i = 0; i < NumPointers; ++i) { |
| for (unsigned j = i+1; j < NumPointers; ++j) { |
| if (!PtrRtCheck.needsChecking(i, j, PtrPartition)) |
| continue; |
| |
| unsigned AS0 = Starts[i]->getType()->getPointerAddressSpace(); |
| unsigned AS1 = Starts[j]->getType()->getPointerAddressSpace(); |
| |
| assert((AS0 == Ends[j]->getType()->getPointerAddressSpace()) && |
| (AS1 == Ends[i]->getType()->getPointerAddressSpace()) && |
| "Trying to bounds check pointers with different address spaces"); |
| |
| Type *PtrArithTy0 = Type::getInt8PtrTy(Ctx, AS0); |
| Type *PtrArithTy1 = Type::getInt8PtrTy(Ctx, AS1); |
| |
| Value *Start0 = ChkBuilder.CreateBitCast(Starts[i], PtrArithTy0, "bc"); |
| Value *Start1 = ChkBuilder.CreateBitCast(Starts[j], PtrArithTy1, "bc"); |
| Value *End0 = ChkBuilder.CreateBitCast(Ends[i], PtrArithTy1, "bc"); |
| Value *End1 = ChkBuilder.CreateBitCast(Ends[j], PtrArithTy0, "bc"); |
| |
| Value *Cmp0 = ChkBuilder.CreateICmpULE(Start0, End1, "bound0"); |
| FirstInst = getFirstInst(FirstInst, Cmp0, Loc); |
| Value *Cmp1 = ChkBuilder.CreateICmpULE(Start1, End0, "bound1"); |
| FirstInst = getFirstInst(FirstInst, Cmp1, Loc); |
| Value *IsConflict = ChkBuilder.CreateAnd(Cmp0, Cmp1, "found.conflict"); |
| FirstInst = getFirstInst(FirstInst, IsConflict, Loc); |
| if (MemoryRuntimeCheck) { |
| IsConflict = ChkBuilder.CreateOr(MemoryRuntimeCheck, IsConflict, |
| "conflict.rdx"); |
| FirstInst = getFirstInst(FirstInst, IsConflict, Loc); |
| } |
| MemoryRuntimeCheck = IsConflict; |
| } |
| } |
| |
| // We have to do this trickery because the IRBuilder might fold the check to a |
| // constant expression in which case there is no Instruction anchored in a |
| // the block. |
| Instruction *Check = BinaryOperator::CreateAnd(MemoryRuntimeCheck, |
| ConstantInt::getTrue(Ctx)); |
| ChkBuilder.Insert(Check, "memcheck.conflict"); |
| FirstInst = getFirstInst(FirstInst, Check, Loc); |
| return std::make_pair(FirstInst, Check); |
| } |
| |
| LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE, |
| const DataLayout &DL, |
| const TargetLibraryInfo *TLI, AliasAnalysis *AA, |
| DominatorTree *DT, |
| const ValueToValueMap &Strides) |
| : DepChecker(SE, L), NumComparisons(0), TheLoop(L), SE(SE), DL(DL), |
| TLI(TLI), AA(AA), DT(DT), NumLoads(0), NumStores(0), |
| MaxSafeDepDistBytes(-1U), CanVecMem(false) { |
| if (canAnalyzeLoop()) |
| analyzeLoop(Strides); |
| } |
| |
| void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const { |
| if (CanVecMem) { |
| if (PtrRtCheck.empty()) |
| OS.indent(Depth) << "Memory dependences are safe\n"; |
| else |
| OS.indent(Depth) << "Memory dependences are safe with run-time checks\n"; |
| } |
| |
| if (Report) |
| OS.indent(Depth) << "Report: " << Report->str() << "\n"; |
| |
| if (auto *InterestingDependences = DepChecker.getInterestingDependences()) { |
| OS.indent(Depth) << "Interesting Dependences:\n"; |
| for (auto &Dep : *InterestingDependences) { |
| Dep.print(OS, Depth + 2, DepChecker.getMemoryInstructions()); |
| OS << "\n"; |
| } |
| } else |
| OS.indent(Depth) << "Too many interesting dependences, not recorded\n"; |
| |
| // List the pair of accesses need run-time checks to prove independence. |
| PtrRtCheck.print(OS, Depth); |
| OS << "\n"; |
| } |
| |
| const LoopAccessInfo & |
| LoopAccessAnalysis::getInfo(Loop *L, const ValueToValueMap &Strides) { |
| auto &LAI = LoopAccessInfoMap[L]; |
| |
| #ifndef NDEBUG |
| assert((!LAI || LAI->NumSymbolicStrides == Strides.size()) && |
| "Symbolic strides changed for loop"); |
| #endif |
| |
| if (!LAI) { |
| const DataLayout &DL = L->getHeader()->getModule()->getDataLayout(); |
| LAI = llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, Strides); |
| #ifndef NDEBUG |
| LAI->NumSymbolicStrides = Strides.size(); |
| #endif |
| } |
| return *LAI.get(); |
| } |
| |
| void LoopAccessAnalysis::print(raw_ostream &OS, const Module *M) const { |
| LoopAccessAnalysis &LAA = *const_cast<LoopAccessAnalysis *>(this); |
| |
| LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| ValueToValueMap NoSymbolicStrides; |
| |
| for (Loop *TopLevelLoop : *LI) |
| for (Loop *L : depth_first(TopLevelLoop)) { |
| OS.indent(2) << L->getHeader()->getName() << ":\n"; |
| auto &LAI = LAA.getInfo(L, NoSymbolicStrides); |
| LAI.print(OS, 4); |
| } |
| } |
| |
| bool LoopAccessAnalysis::runOnFunction(Function &F) { |
| SE = &getAnalysis<ScalarEvolution>(); |
| auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>(); |
| TLI = TLIP ? &TLIP->getTLI() : nullptr; |
| AA = &getAnalysis<AliasAnalysis>(); |
| DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| |
| return false; |
| } |
| |
| void LoopAccessAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<ScalarEvolution>(); |
| AU.addRequired<AliasAnalysis>(); |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.addRequired<LoopInfoWrapperPass>(); |
| |
| AU.setPreservesAll(); |
| } |
| |
| char LoopAccessAnalysis::ID = 0; |
| static const char laa_name[] = "Loop Access Analysis"; |
| #define LAA_NAME "loop-accesses" |
| |
| INITIALIZE_PASS_BEGIN(LoopAccessAnalysis, LAA_NAME, laa_name, false, true) |
| INITIALIZE_AG_DEPENDENCY(AliasAnalysis) |
| INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) |
| INITIALIZE_PASS_END(LoopAccessAnalysis, LAA_NAME, laa_name, false, true) |
| |
| namespace llvm { |
| Pass *createLAAPass() { |
| return new LoopAccessAnalysis(); |
| } |
| } |