| //===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // The implementation for the loop memory dependence that was originally |
| // developed for the loop vectorizer. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/LoopAccessAnalysis.h" |
| #include "llvm/ADT/APInt.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/DepthFirstIterator.h" |
| #include "llvm/ADT/EquivalenceClasses.h" |
| #include "llvm/ADT/PointerIntPair.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/iterator_range.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/AliasSetTracker.h" |
| #include "llvm/Analysis/LoopAnalysisManager.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopIterator.h" |
| #include "llvm/Analysis/MemoryLocation.h" |
| #include "llvm/Analysis/OptimizationRemarkEmitter.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/Analysis/ScalarEvolutionExpressions.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/Analysis/VectorUtils.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DebugLoc.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/DiagnosticInfo.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/InstrTypes.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/Operator.h" |
| #include "llvm/IR/PassManager.h" |
| #include "llvm/IR/PatternMatch.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/IR/Value.h" |
| #include "llvm/IR/ValueHandle.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <algorithm> |
| #include <cassert> |
| #include <cstdint> |
| #include <iterator> |
| #include <utility> |
| #include <vector> |
| |
| using namespace llvm; |
| using namespace llvm::PatternMatch; |
| |
| #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; |
| |
| /// The maximum iterations used to merge memory checks |
| static cl::opt<unsigned> MemoryCheckMergeThreshold( |
| "memory-check-merge-threshold", cl::Hidden, |
| cl::desc("Maximum number of comparisons done when trying to merge " |
| "runtime memory checks. (default = 100)"), |
| cl::init(100)); |
| |
| /// Maximum SIMD width. |
| const unsigned VectorizerParams::MaxVectorWidth = 64; |
| |
| /// We collect dependences up to this threshold. |
| static cl::opt<unsigned> |
| MaxDependences("max-dependences", cl::Hidden, |
| cl::desc("Maximum number of dependences collected by " |
| "loop-access analysis (default = 100)"), |
| cl::init(100)); |
| |
| /// This enables versioning on the strides of symbolically striding memory |
| /// accesses in code like the following. |
| /// for (i = 0; i < N; ++i) |
| /// A[i * Stride1] += B[i * Stride2] ... |
| /// |
| /// Will be roughly translated to |
| /// if (Stride1 == 1 && Stride2 == 1) { |
| /// for (i = 0; i < N; i+=4) |
| /// A[i:i+3] += ... |
| /// } else |
| /// ... |
| static cl::opt<bool> EnableMemAccessVersioning( |
| "enable-mem-access-versioning", cl::init(true), cl::Hidden, |
| cl::desc("Enable symbolic stride memory access versioning")); |
| |
| /// Enable store-to-load forwarding conflict detection. This option can |
| /// be disabled for correctness testing. |
| static cl::opt<bool> EnableForwardingConflictDetection( |
| "store-to-load-forwarding-conflict-detection", cl::Hidden, |
| cl::desc("Enable conflict detection in loop-access analysis"), |
| cl::init(true)); |
| |
| static cl::opt<unsigned> MaxForkedSCEVDepth( |
| "max-forked-scev-depth", cl::Hidden, |
| cl::desc("Maximum recursion depth when finding forked SCEVs (default = 5)"), |
| cl::init(5)); |
| |
| bool VectorizerParams::isInterleaveForced() { |
| return ::VectorizationInterleave.getNumOccurrences() > 0; |
| } |
| |
| Value *llvm::stripIntegerCast(Value *V) { |
| if (auto *CI = dyn_cast<CastInst>(V)) |
| if (CI->getOperand(0)->getType()->isIntegerTy()) |
| return CI->getOperand(0); |
| return V; |
| } |
| |
| const SCEV *llvm::replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE, |
| const ValueToValueMap &PtrToStride, |
| Value *Ptr) { |
| const SCEV *OrigSCEV = PSE.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(Ptr); |
| if (SI == PtrToStride.end()) |
| // For a non-symbolic stride, just return the original expression. |
| return OrigSCEV; |
| |
| Value *StrideVal = stripIntegerCast(SI->second); |
| |
| ScalarEvolution *SE = PSE.getSE(); |
| const auto *U = cast<SCEVUnknown>(SE->getSCEV(StrideVal)); |
| const auto *CT = |
| static_cast<const SCEVConstant *>(SE->getOne(StrideVal->getType())); |
| |
| PSE.addPredicate(*SE->getEqualPredicate(U, CT)); |
| auto *Expr = PSE.getSCEV(Ptr); |
| |
| LLVM_DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEV |
| << " by: " << *Expr << "\n"); |
| return Expr; |
| } |
| |
| RuntimeCheckingPtrGroup::RuntimeCheckingPtrGroup( |
| unsigned Index, RuntimePointerChecking &RtCheck) |
| : High(RtCheck.Pointers[Index].End), Low(RtCheck.Pointers[Index].Start), |
| AddressSpace(RtCheck.Pointers[Index] |
| .PointerValue->getType() |
| ->getPointerAddressSpace()), |
| NeedsFreeze(RtCheck.Pointers[Index].NeedsFreeze) { |
| Members.push_back(Index); |
| } |
| |
| /// Calculate Start and End points of memory access. |
| /// Let's assume A is the first access and B is a memory access on N-th loop |
| /// iteration. Then B is calculated as: |
| /// B = A + Step*N . |
| /// Step value may be positive or negative. |
| /// N is a calculated back-edge taken count: |
| /// N = (TripCount > 0) ? RoundDown(TripCount -1 , VF) : 0 |
| /// Start and End points are calculated in the following way: |
| /// Start = UMIN(A, B) ; End = UMAX(A, B) + SizeOfElt, |
| /// where SizeOfElt is the size of single memory access in bytes. |
| /// |
| /// There is no conflict when the intervals are disjoint: |
| /// NoConflict = (P2.Start >= P1.End) || (P1.Start >= P2.End) |
| void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, const SCEV *PtrExpr, |
| Type *AccessTy, bool WritePtr, |
| unsigned DepSetId, unsigned ASId, |
| PredicatedScalarEvolution &PSE, |
| bool NeedsFreeze) { |
| ScalarEvolution *SE = PSE.getSE(); |
| |
| const SCEV *ScStart; |
| const SCEV *ScEnd; |
| |
| if (SE->isLoopInvariant(PtrExpr, Lp)) { |
| ScStart = ScEnd = PtrExpr; |
| } else { |
| const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrExpr); |
| assert(AR && "Invalid addrec expression"); |
| const SCEV *Ex = PSE.getBackedgeTakenCount(); |
| |
| ScStart = AR->getStart(); |
| ScEnd = AR->evaluateAtIteration(Ex, *SE); |
| const SCEV *Step = AR->getStepRecurrence(*SE); |
| |
| // For expressions with negative step, the upper bound is ScStart and the |
| // lower bound is ScEnd. |
| if (const auto *CStep = dyn_cast<SCEVConstant>(Step)) { |
| if (CStep->getValue()->isNegative()) |
| std::swap(ScStart, ScEnd); |
| } else { |
| // Fallback case: the step is not constant, but we can still |
| // get the upper and lower bounds of the interval by using min/max |
| // expressions. |
| ScStart = SE->getUMinExpr(ScStart, ScEnd); |
| ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd); |
| } |
| } |
| // Add the size of the pointed element to ScEnd. |
| auto &DL = Lp->getHeader()->getModule()->getDataLayout(); |
| Type *IdxTy = DL.getIndexType(Ptr->getType()); |
| const SCEV *EltSizeSCEV = SE->getStoreSizeOfExpr(IdxTy, AccessTy); |
| ScEnd = SE->getAddExpr(ScEnd, EltSizeSCEV); |
| |
| Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, PtrExpr, |
| NeedsFreeze); |
| } |
| |
| void RuntimePointerChecking::tryToCreateDiffCheck( |
| const RuntimeCheckingPtrGroup &CGI, const RuntimeCheckingPtrGroup &CGJ) { |
| if (!CanUseDiffCheck) |
| return; |
| |
| // If either group contains multiple different pointers, bail out. |
| // TODO: Support multiple pointers by using the minimum or maximum pointer, |
| // depending on src & sink. |
| if (CGI.Members.size() != 1 || CGJ.Members.size() != 1) { |
| CanUseDiffCheck = false; |
| return; |
| } |
| |
| PointerInfo *Src = &Pointers[CGI.Members[0]]; |
| PointerInfo *Sink = &Pointers[CGJ.Members[0]]; |
| |
| // If either pointer is read and written, multiple checks may be needed. Bail |
| // out. |
| if (!DC.getOrderForAccess(Src->PointerValue, !Src->IsWritePtr).empty() || |
| !DC.getOrderForAccess(Sink->PointerValue, !Sink->IsWritePtr).empty()) { |
| CanUseDiffCheck = false; |
| return; |
| } |
| |
| ArrayRef<unsigned> AccSrc = |
| DC.getOrderForAccess(Src->PointerValue, Src->IsWritePtr); |
| ArrayRef<unsigned> AccSink = |
| DC.getOrderForAccess(Sink->PointerValue, Sink->IsWritePtr); |
| // If either pointer is accessed multiple times, there may not be a clear |
| // src/sink relation. Bail out for now. |
| if (AccSrc.size() != 1 || AccSink.size() != 1) { |
| CanUseDiffCheck = false; |
| return; |
| } |
| // If the sink is accessed before src, swap src/sink. |
| if (AccSink[0] < AccSrc[0]) |
| std::swap(Src, Sink); |
| |
| auto *SrcAR = dyn_cast<SCEVAddRecExpr>(Src->Expr); |
| auto *SinkAR = dyn_cast<SCEVAddRecExpr>(Sink->Expr); |
| if (!SrcAR || !SinkAR || SrcAR->getLoop() != DC.getInnermostLoop() || |
| SinkAR->getLoop() != DC.getInnermostLoop()) { |
| CanUseDiffCheck = false; |
| return; |
| } |
| |
| SmallVector<Instruction *, 4> SrcInsts = |
| DC.getInstructionsForAccess(Src->PointerValue, Src->IsWritePtr); |
| SmallVector<Instruction *, 4> SinkInsts = |
| DC.getInstructionsForAccess(Sink->PointerValue, Sink->IsWritePtr); |
| Type *SrcTy = getLoadStoreType(SrcInsts[0]); |
| Type *DstTy = getLoadStoreType(SinkInsts[0]); |
| if (isa<ScalableVectorType>(SrcTy) || isa<ScalableVectorType>(DstTy)) { |
| CanUseDiffCheck = false; |
| return; |
| } |
| const DataLayout &DL = |
| SinkAR->getLoop()->getHeader()->getModule()->getDataLayout(); |
| unsigned AllocSize = |
| std::max(DL.getTypeAllocSize(SrcTy), DL.getTypeAllocSize(DstTy)); |
| |
| // Only matching constant steps matching the AllocSize are supported at the |
| // moment. This simplifies the difference computation. Can be extended in the |
| // future. |
| auto *Step = dyn_cast<SCEVConstant>(SinkAR->getStepRecurrence(*SE)); |
| if (!Step || Step != SrcAR->getStepRecurrence(*SE) || |
| Step->getAPInt().abs() != AllocSize) { |
| CanUseDiffCheck = false; |
| return; |
| } |
| |
| IntegerType *IntTy = |
| IntegerType::get(Src->PointerValue->getContext(), |
| DL.getPointerSizeInBits(CGI.AddressSpace)); |
| |
| // When counting down, the dependence distance needs to be swapped. |
| if (Step->getValue()->isNegative()) |
| std::swap(SinkAR, SrcAR); |
| |
| const SCEV *SinkStartInt = SE->getPtrToIntExpr(SinkAR->getStart(), IntTy); |
| const SCEV *SrcStartInt = SE->getPtrToIntExpr(SrcAR->getStart(), IntTy); |
| if (isa<SCEVCouldNotCompute>(SinkStartInt) || |
| isa<SCEVCouldNotCompute>(SrcStartInt)) { |
| CanUseDiffCheck = false; |
| return; |
| } |
| DiffChecks.emplace_back(SrcStartInt, SinkStartInt, AllocSize, |
| Src->NeedsFreeze || Sink->NeedsFreeze); |
| } |
| |
| SmallVector<RuntimePointerCheck, 4> RuntimePointerChecking::generateChecks() { |
| SmallVector<RuntimePointerCheck, 4> Checks; |
| |
| for (unsigned I = 0; I < CheckingGroups.size(); ++I) { |
| for (unsigned J = I + 1; J < CheckingGroups.size(); ++J) { |
| const RuntimeCheckingPtrGroup &CGI = CheckingGroups[I]; |
| const RuntimeCheckingPtrGroup &CGJ = CheckingGroups[J]; |
| |
| if (needsChecking(CGI, CGJ)) { |
| tryToCreateDiffCheck(CGI, CGJ); |
| Checks.push_back(std::make_pair(&CGI, &CGJ)); |
| } |
| } |
| } |
| return Checks; |
| } |
| |
| void RuntimePointerChecking::generateChecks( |
| MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) { |
| assert(Checks.empty() && "Checks is not empty"); |
| groupChecks(DepCands, UseDependencies); |
| Checks = generateChecks(); |
| } |
| |
| bool RuntimePointerChecking::needsChecking( |
| const RuntimeCheckingPtrGroup &M, const RuntimeCheckingPtrGroup &N) const { |
| for (unsigned I = 0, EI = M.Members.size(); EI != I; ++I) |
| for (unsigned J = 0, EJ = N.Members.size(); EJ != J; ++J) |
| if (needsChecking(M.Members[I], N.Members[J])) |
| return true; |
| return false; |
| } |
| |
| /// Compare \p I and \p J and return the minimum. |
| /// Return nullptr in case we couldn't find an answer. |
| static const SCEV *getMinFromExprs(const SCEV *I, const SCEV *J, |
| ScalarEvolution *SE) { |
| const SCEV *Diff = SE->getMinusSCEV(J, I); |
| const SCEVConstant *C = dyn_cast<const SCEVConstant>(Diff); |
| |
| if (!C) |
| return nullptr; |
| if (C->getValue()->isNegative()) |
| return J; |
| return I; |
| } |
| |
| bool RuntimeCheckingPtrGroup::addPointer(unsigned Index, |
| RuntimePointerChecking &RtCheck) { |
| return addPointer( |
| Index, RtCheck.Pointers[Index].Start, RtCheck.Pointers[Index].End, |
| RtCheck.Pointers[Index].PointerValue->getType()->getPointerAddressSpace(), |
| RtCheck.Pointers[Index].NeedsFreeze, *RtCheck.SE); |
| } |
| |
| bool RuntimeCheckingPtrGroup::addPointer(unsigned Index, const SCEV *Start, |
| const SCEV *End, unsigned AS, |
| bool NeedsFreeze, |
| ScalarEvolution &SE) { |
| assert(AddressSpace == AS && |
| "all pointers in a checking group must be in the same address space"); |
| |
| // Compare the starts and ends with the known minimum and maximum |
| // of this set. We need to know how we compare against the min/max |
| // of the set in order to be able to emit memchecks. |
| const SCEV *Min0 = getMinFromExprs(Start, Low, &SE); |
| if (!Min0) |
| return false; |
| |
| const SCEV *Min1 = getMinFromExprs(End, High, &SE); |
| if (!Min1) |
| return false; |
| |
| // Update the low bound expression if we've found a new min value. |
| if (Min0 == Start) |
| Low = Start; |
| |
| // Update the high bound expression if we've found a new max value. |
| if (Min1 != End) |
| High = End; |
| |
| Members.push_back(Index); |
| this->NeedsFreeze |= NeedsFreeze; |
| return true; |
| } |
| |
| void RuntimePointerChecking::groupChecks( |
| MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) { |
| // We build the groups from dependency candidates equivalence classes |
| // because: |
| // - We know that pointers in the same equivalence class share |
| // the same underlying object and therefore there is a chance |
| // that we can compare pointers |
| // - We wouldn't be able to merge two pointers for which we need |
| // to emit a memcheck. The classes in DepCands are already |
| // conveniently built such that no two pointers in the same |
| // class need checking against each other. |
| |
| // We use the following (greedy) algorithm to construct the groups |
| // For every pointer in the equivalence class: |
| // For each existing group: |
| // - if the difference between this pointer and the min/max bounds |
| // of the group is a constant, then make the pointer part of the |
| // group and update the min/max bounds of that group as required. |
| |
| CheckingGroups.clear(); |
| |
| // If we need to check two pointers to the same underlying object |
| // with a non-constant difference, we shouldn't perform any pointer |
| // grouping with those pointers. This is because we can easily get |
| // into cases where the resulting check would return false, even when |
| // the accesses are safe. |
| // |
| // The following example shows this: |
| // for (i = 0; i < 1000; ++i) |
| // a[5000 + i * m] = a[i] + a[i + 9000] |
| // |
| // Here grouping gives a check of (5000, 5000 + 1000 * m) against |
| // (0, 10000) which is always false. However, if m is 1, there is no |
| // dependence. Not grouping the checks for a[i] and a[i + 9000] allows |
| // us to perform an accurate check in this case. |
| // |
| // The above case requires that we have an UnknownDependence between |
| // accesses to the same underlying object. This cannot happen unless |
| // FoundNonConstantDistanceDependence is set, and therefore UseDependencies |
| // is also false. In this case we will use the fallback path and create |
| // separate checking groups for all pointers. |
| |
| // If we don't have the dependency partitions, construct a new |
| // checking pointer group for each pointer. This is also required |
| // for correctness, because in this case we can have checking between |
| // pointers to the same underlying object. |
| if (!UseDependencies) { |
| for (unsigned I = 0; I < Pointers.size(); ++I) |
| CheckingGroups.push_back(RuntimeCheckingPtrGroup(I, *this)); |
| return; |
| } |
| |
| unsigned TotalComparisons = 0; |
| |
| DenseMap<Value *, SmallVector<unsigned>> PositionMap; |
| for (unsigned Index = 0; Index < Pointers.size(); ++Index) { |
| auto Iter = PositionMap.insert({Pointers[Index].PointerValue, {}}); |
| Iter.first->second.push_back(Index); |
| } |
| |
| // We need to keep track of what pointers we've already seen so we |
| // don't process them twice. |
| SmallSet<unsigned, 2> Seen; |
| |
| // Go through all equivalence classes, get the "pointer check groups" |
| // and add them to the overall solution. We use the order in which accesses |
| // appear in 'Pointers' to enforce determinism. |
| for (unsigned I = 0; I < Pointers.size(); ++I) { |
| // We've seen this pointer before, and therefore already processed |
| // its equivalence class. |
| if (Seen.count(I)) |
| continue; |
| |
| MemoryDepChecker::MemAccessInfo Access(Pointers[I].PointerValue, |
| Pointers[I].IsWritePtr); |
| |
| SmallVector<RuntimeCheckingPtrGroup, 2> Groups; |
| auto LeaderI = DepCands.findValue(DepCands.getLeaderValue(Access)); |
| |
| // Because DepCands is constructed by visiting accesses in the order in |
| // which they appear in alias sets (which is deterministic) and the |
| // iteration order within an equivalence class member is only dependent on |
| // the order in which unions and insertions are performed on the |
| // equivalence class, the iteration order is deterministic. |
| for (auto MI = DepCands.member_begin(LeaderI), ME = DepCands.member_end(); |
| MI != ME; ++MI) { |
| auto PointerI = PositionMap.find(MI->getPointer()); |
| assert(PointerI != PositionMap.end() && |
| "pointer in equivalence class not found in PositionMap"); |
| for (unsigned Pointer : PointerI->second) { |
| bool Merged = false; |
| // Mark this pointer as seen. |
| Seen.insert(Pointer); |
| |
| // Go through all the existing sets and see if we can find one |
| // which can include this pointer. |
| for (RuntimeCheckingPtrGroup &Group : Groups) { |
| // Don't perform more than a certain amount of comparisons. |
| // This should limit the cost of grouping the pointers to something |
| // reasonable. If we do end up hitting this threshold, the algorithm |
| // will create separate groups for all remaining pointers. |
| if (TotalComparisons > MemoryCheckMergeThreshold) |
| break; |
| |
| TotalComparisons++; |
| |
| if (Group.addPointer(Pointer, *this)) { |
| Merged = true; |
| break; |
| } |
| } |
| |
| if (!Merged) |
| // We couldn't add this pointer to any existing set or the threshold |
| // for the number of comparisons has been reached. Create a new group |
| // to hold the current pointer. |
| Groups.push_back(RuntimeCheckingPtrGroup(Pointer, *this)); |
| } |
| } |
| |
| // We've computed the grouped checks for this partition. |
| // Save the results and continue with the next one. |
| llvm::copy(Groups, std::back_inserter(CheckingGroups)); |
| } |
| } |
| |
| bool RuntimePointerChecking::arePointersInSamePartition( |
| const SmallVectorImpl<int> &PtrToPartition, unsigned PtrIdx1, |
| unsigned PtrIdx2) { |
| return (PtrToPartition[PtrIdx1] != -1 && |
| PtrToPartition[PtrIdx1] == PtrToPartition[PtrIdx2]); |
| } |
| |
| bool RuntimePointerChecking::needsChecking(unsigned I, unsigned J) const { |
| const PointerInfo &PointerI = Pointers[I]; |
| const PointerInfo &PointerJ = Pointers[J]; |
| |
| // No need to check if two readonly pointers intersect. |
| if (!PointerI.IsWritePtr && !PointerJ.IsWritePtr) |
| return false; |
| |
| // Only need to check pointers between two different dependency sets. |
| if (PointerI.DependencySetId == PointerJ.DependencySetId) |
| return false; |
| |
| // Only need to check pointers in the same alias set. |
| if (PointerI.AliasSetId != PointerJ.AliasSetId) |
| return false; |
| |
| return true; |
| } |
| |
| void RuntimePointerChecking::printChecks( |
| raw_ostream &OS, const SmallVectorImpl<RuntimePointerCheck> &Checks, |
| unsigned Depth) const { |
| unsigned N = 0; |
| for (const auto &Check : Checks) { |
| const auto &First = Check.first->Members, &Second = Check.second->Members; |
| |
| OS.indent(Depth) << "Check " << N++ << ":\n"; |
| |
| OS.indent(Depth + 2) << "Comparing group (" << Check.first << "):\n"; |
| for (unsigned K = 0; K < First.size(); ++K) |
| OS.indent(Depth + 2) << *Pointers[First[K]].PointerValue << "\n"; |
| |
| OS.indent(Depth + 2) << "Against group (" << Check.second << "):\n"; |
| for (unsigned K = 0; K < Second.size(); ++K) |
| OS.indent(Depth + 2) << *Pointers[Second[K]].PointerValue << "\n"; |
| } |
| } |
| |
| void RuntimePointerChecking::print(raw_ostream &OS, unsigned Depth) const { |
| |
| OS.indent(Depth) << "Run-time memory checks:\n"; |
| printChecks(OS, Checks, Depth); |
| |
| OS.indent(Depth) << "Grouped accesses:\n"; |
| for (unsigned I = 0; I < CheckingGroups.size(); ++I) { |
| const auto &CG = CheckingGroups[I]; |
| |
| OS.indent(Depth + 2) << "Group " << &CG << ":\n"; |
| OS.indent(Depth + 4) << "(Low: " << *CG.Low << " High: " << *CG.High |
| << ")\n"; |
| for (unsigned J = 0; J < CG.Members.size(); ++J) { |
| OS.indent(Depth + 6) << "Member: " << *Pointers[CG.Members[J]].Expr |
| << "\n"; |
| } |
| } |
| } |
| |
| namespace { |
| |
| /// Analyses memory accesses in a loop. |
| /// |
| /// Checks whether run time pointer checks are needed and builds sets for data |
| /// dependence checking. |
| class AccessAnalysis { |
| public: |
| /// Read or write access location. |
| typedef PointerIntPair<Value *, 1, bool> MemAccessInfo; |
| typedef SmallVector<MemAccessInfo, 8> MemAccessInfoList; |
| |
| AccessAnalysis(Loop *TheLoop, AAResults *AA, LoopInfo *LI, |
| MemoryDepChecker::DepCandidates &DA, |
| PredicatedScalarEvolution &PSE) |
| : TheLoop(TheLoop), BAA(*AA), AST(BAA), LI(LI), DepCands(DA), PSE(PSE) { |
| // We're analyzing dependences across loop iterations. |
| BAA.enableCrossIterationMode(); |
| } |
| |
| /// Register a load and whether it is only read from. |
| void addLoad(MemoryLocation &Loc, Type *AccessTy, bool IsReadOnly) { |
| Value *Ptr = const_cast<Value*>(Loc.Ptr); |
| AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags); |
| Accesses[MemAccessInfo(Ptr, false)].insert(AccessTy); |
| if (IsReadOnly) |
| ReadOnlyPtr.insert(Ptr); |
| } |
| |
| /// Register a store. |
| void addStore(MemoryLocation &Loc, Type *AccessTy) { |
| Value *Ptr = const_cast<Value*>(Loc.Ptr); |
| AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags); |
| Accesses[MemAccessInfo(Ptr, true)].insert(AccessTy); |
| } |
| |
| /// Check if we can emit a run-time no-alias check for \p Access. |
| /// |
| /// Returns true if we can emit a run-time no alias check for \p Access. |
| /// If we can check this access, this also adds it to a dependence set and |
| /// adds a run-time to check for it to \p RtCheck. If \p Assume is true, |
| /// we will attempt to use additional run-time checks in order to get |
| /// the bounds of the pointer. |
| bool createCheckForAccess(RuntimePointerChecking &RtCheck, |
| MemAccessInfo Access, Type *AccessTy, |
| const ValueToValueMap &Strides, |
| DenseMap<Value *, unsigned> &DepSetId, |
| Loop *TheLoop, unsigned &RunningDepId, |
| unsigned ASId, bool ShouldCheckStride, bool Assume); |
| |
| /// Check whether we can check the pointers at runtime for |
| /// non-intersection. |
| /// |
| /// Returns true if we need no check or if we do and we can generate them |
| /// (i.e. the pointers have computable bounds). |
| bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE, |
| Loop *TheLoop, const ValueToValueMap &Strides, |
| Value *&UncomputablePtr, bool ShouldCheckWrap = false); |
| |
| /// Goes over all memory accesses, checks whether a RT check is needed |
| /// and builds sets of dependent accesses. |
| void buildDependenceSets() { |
| processMemAccesses(); |
| } |
| |
| /// Initial processing of memory accesses determined that we need to |
| /// perform dependency checking. |
| /// |
| /// Note that this can later be cleared if we retry memcheck analysis without |
| /// dependency checking (i.e. FoundNonConstantDistanceDependence). |
| bool isDependencyCheckNeeded() { return !CheckDeps.empty(); } |
| |
| /// We decided that no dependence analysis would be used. Reset the state. |
| void resetDepChecks(MemoryDepChecker &DepChecker) { |
| CheckDeps.clear(); |
| DepChecker.clearDependences(); |
| } |
| |
| MemAccessInfoList &getDependenciesToCheck() { return CheckDeps; } |
| |
| private: |
| typedef MapVector<MemAccessInfo, SmallSetVector<Type *, 1>> PtrAccessMap; |
| |
| /// Go over all memory access and check whether runtime pointer checks |
| /// are needed and build sets of dependency check candidates. |
| void processMemAccesses(); |
| |
| /// Map of all accesses. Values are the types used to access memory pointed to |
| /// by the pointer. |
| PtrAccessMap Accesses; |
| |
| /// The loop being checked. |
| const Loop *TheLoop; |
| |
| /// List of accesses that need a further dependence check. |
| MemAccessInfoList CheckDeps; |
| |
| /// Set of pointers that are read only. |
| SmallPtrSet<Value*, 16> ReadOnlyPtr; |
| |
| /// Batched alias analysis results. |
| BatchAAResults BAA; |
| |
| /// An alias set tracker to partition the access set by underlying object and |
| //intrinsic property (such as TBAA metadata). |
| AliasSetTracker AST; |
| |
| LoopInfo *LI; |
| |
| /// 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; |
| |
| /// Initial processing of memory accesses determined that we may need |
| /// to add memchecks. Perform the analysis to determine the necessary checks. |
| /// |
| /// Note that, this is different from isDependencyCheckNeeded. When we retry |
| /// memcheck analysis without dependency checking |
| /// (i.e. FoundNonConstantDistanceDependence), isDependencyCheckNeeded is |
| /// cleared while this remains set if we have potentially dependent accesses. |
| bool IsRTCheckAnalysisNeeded = false; |
| |
| /// The SCEV predicate containing all the SCEV-related assumptions. |
| PredicatedScalarEvolution &PSE; |
| }; |
| |
| } // end anonymous namespace |
| |
| /// Check whether a pointer can participate in a runtime bounds check. |
| /// If \p Assume, try harder to prove that we can compute the bounds of \p Ptr |
| /// by adding run-time checks (overflow checks) if necessary. |
| static bool hasComputableBounds(PredicatedScalarEvolution &PSE, Value *Ptr, |
| const SCEV *PtrScev, Loop *L, bool Assume) { |
| // The bounds for loop-invariant pointer is trivial. |
| if (PSE.getSE()->isLoopInvariant(PtrScev, L)) |
| return true; |
| |
| const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); |
| |
| if (!AR && Assume) |
| AR = PSE.getAsAddRec(Ptr); |
| |
| if (!AR) |
| return false; |
| |
| return AR->isAffine(); |
| } |
| |
| /// Check whether a pointer address cannot wrap. |
| static bool isNoWrap(PredicatedScalarEvolution &PSE, |
| const ValueToValueMap &Strides, Value *Ptr, Type *AccessTy, |
| Loop *L) { |
| const SCEV *PtrScev = PSE.getSCEV(Ptr); |
| if (PSE.getSE()->isLoopInvariant(PtrScev, L)) |
| return true; |
| |
| int64_t Stride = getPtrStride(PSE, AccessTy, Ptr, L, Strides).value_or(0); |
| if (Stride == 1 || PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW)) |
| return true; |
| |
| return false; |
| } |
| |
| static void visitPointers(Value *StartPtr, const Loop &InnermostLoop, |
| function_ref<void(Value *)> AddPointer) { |
| SmallPtrSet<Value *, 8> Visited; |
| SmallVector<Value *> WorkList; |
| WorkList.push_back(StartPtr); |
| |
| while (!WorkList.empty()) { |
| Value *Ptr = WorkList.pop_back_val(); |
| if (!Visited.insert(Ptr).second) |
| continue; |
| auto *PN = dyn_cast<PHINode>(Ptr); |
| // SCEV does not look through non-header PHIs inside the loop. Such phis |
| // can be analyzed by adding separate accesses for each incoming pointer |
| // value. |
| if (PN && InnermostLoop.contains(PN->getParent()) && |
| PN->getParent() != InnermostLoop.getHeader()) { |
| for (const Use &Inc : PN->incoming_values()) |
| WorkList.push_back(Inc); |
| } else |
| AddPointer(Ptr); |
| } |
| } |
| |
| // Walk back through the IR for a pointer, looking for a select like the |
| // following: |
| // |
| // %offset = select i1 %cmp, i64 %a, i64 %b |
| // %addr = getelementptr double, double* %base, i64 %offset |
| // %ld = load double, double* %addr, align 8 |
| // |
| // We won't be able to form a single SCEVAddRecExpr from this since the |
| // address for each loop iteration depends on %cmp. We could potentially |
| // produce multiple valid SCEVAddRecExprs, though, and check all of them for |
| // memory safety/aliasing if needed. |
| // |
| // If we encounter some IR we don't yet handle, or something obviously fine |
| // like a constant, then we just add the SCEV for that term to the list passed |
| // in by the caller. If we have a node that may potentially yield a valid |
| // SCEVAddRecExpr then we decompose it into parts and build the SCEV terms |
| // ourselves before adding to the list. |
| static void findForkedSCEVs( |
| ScalarEvolution *SE, const Loop *L, Value *Ptr, |
| SmallVectorImpl<PointerIntPair<const SCEV *, 1, bool>> &ScevList, |
| unsigned Depth) { |
| // If our Value is a SCEVAddRecExpr, loop invariant, not an instruction, or |
| // we've exceeded our limit on recursion, just return whatever we have |
| // regardless of whether it can be used for a forked pointer or not, along |
| // with an indication of whether it might be a poison or undef value. |
| const SCEV *Scev = SE->getSCEV(Ptr); |
| if (isa<SCEVAddRecExpr>(Scev) || L->isLoopInvariant(Ptr) || |
| !isa<Instruction>(Ptr) || Depth == 0) { |
| ScevList.emplace_back(Scev, !isGuaranteedNotToBeUndefOrPoison(Ptr)); |
| return; |
| } |
| |
| Depth--; |
| |
| auto UndefPoisonCheck = [](PointerIntPair<const SCEV *, 1, bool> S) { |
| return get<1>(S); |
| }; |
| |
| auto GetBinOpExpr = [&SE](unsigned Opcode, const SCEV *L, const SCEV *R) { |
| switch (Opcode) { |
| case Instruction::Add: |
| return SE->getAddExpr(L, R); |
| case Instruction::Sub: |
| return SE->getMinusSCEV(L, R); |
| default: |
| llvm_unreachable("Unexpected binary operator when walking ForkedPtrs"); |
| } |
| }; |
| |
| Instruction *I = cast<Instruction>(Ptr); |
| unsigned Opcode = I->getOpcode(); |
| switch (Opcode) { |
| case Instruction::GetElementPtr: { |
| GetElementPtrInst *GEP = cast<GetElementPtrInst>(I); |
| Type *SourceTy = GEP->getSourceElementType(); |
| // We only handle base + single offset GEPs here for now. |
| // Not dealing with preexisting gathers yet, so no vectors. |
| if (I->getNumOperands() != 2 || SourceTy->isVectorTy()) { |
| ScevList.emplace_back(Scev, !isGuaranteedNotToBeUndefOrPoison(GEP)); |
| break; |
| } |
| SmallVector<PointerIntPair<const SCEV *, 1, bool>, 2> BaseScevs; |
| SmallVector<PointerIntPair<const SCEV *, 1, bool>, 2> OffsetScevs; |
| findForkedSCEVs(SE, L, I->getOperand(0), BaseScevs, Depth); |
| findForkedSCEVs(SE, L, I->getOperand(1), OffsetScevs, Depth); |
| |
| // See if we need to freeze our fork... |
| bool NeedsFreeze = any_of(BaseScevs, UndefPoisonCheck) || |
| any_of(OffsetScevs, UndefPoisonCheck); |
| |
| // Check that we only have a single fork, on either the base or the offset. |
| // Copy the SCEV across for the one without a fork in order to generate |
| // the full SCEV for both sides of the GEP. |
| if (OffsetScevs.size() == 2 && BaseScevs.size() == 1) |
| BaseScevs.push_back(BaseScevs[0]); |
| else if (BaseScevs.size() == 2 && OffsetScevs.size() == 1) |
| OffsetScevs.push_back(OffsetScevs[0]); |
| else { |
| ScevList.emplace_back(Scev, NeedsFreeze); |
| break; |
| } |
| |
| // Find the pointer type we need to extend to. |
| Type *IntPtrTy = SE->getEffectiveSCEVType( |
| SE->getSCEV(GEP->getPointerOperand())->getType()); |
| |
| // Find the size of the type being pointed to. We only have a single |
| // index term (guarded above) so we don't need to index into arrays or |
| // structures, just get the size of the scalar value. |
| const SCEV *Size = SE->getSizeOfExpr(IntPtrTy, SourceTy); |
| |
| // Scale up the offsets by the size of the type, then add to the bases. |
| const SCEV *Scaled1 = SE->getMulExpr( |
| Size, SE->getTruncateOrSignExtend(get<0>(OffsetScevs[0]), IntPtrTy)); |
| const SCEV *Scaled2 = SE->getMulExpr( |
| Size, SE->getTruncateOrSignExtend(get<0>(OffsetScevs[1]), IntPtrTy)); |
| ScevList.emplace_back(SE->getAddExpr(get<0>(BaseScevs[0]), Scaled1), |
| NeedsFreeze); |
| ScevList.emplace_back(SE->getAddExpr(get<0>(BaseScevs[1]), Scaled2), |
| NeedsFreeze); |
| break; |
| } |
| case Instruction::Select: { |
| SmallVector<PointerIntPair<const SCEV *, 1, bool>, 2> ChildScevs; |
| // A select means we've found a forked pointer, but we currently only |
| // support a single select per pointer so if there's another behind this |
| // then we just bail out and return the generic SCEV. |
| findForkedSCEVs(SE, L, I->getOperand(1), ChildScevs, Depth); |
| findForkedSCEVs(SE, L, I->getOperand(2), ChildScevs, Depth); |
| if (ChildScevs.size() == 2) { |
| ScevList.push_back(ChildScevs[0]); |
| ScevList.push_back(ChildScevs[1]); |
| } else |
| ScevList.emplace_back(Scev, !isGuaranteedNotToBeUndefOrPoison(Ptr)); |
| break; |
| } |
| case Instruction::Add: |
| case Instruction::Sub: { |
| SmallVector<PointerIntPair<const SCEV *, 1, bool>> LScevs; |
| SmallVector<PointerIntPair<const SCEV *, 1, bool>> RScevs; |
| findForkedSCEVs(SE, L, I->getOperand(0), LScevs, Depth); |
| findForkedSCEVs(SE, L, I->getOperand(1), RScevs, Depth); |
| |
| // See if we need to freeze our fork... |
| bool NeedsFreeze = |
| any_of(LScevs, UndefPoisonCheck) || any_of(RScevs, UndefPoisonCheck); |
| |
| // Check that we only have a single fork, on either the left or right side. |
| // Copy the SCEV across for the one without a fork in order to generate |
| // the full SCEV for both sides of the BinOp. |
| if (LScevs.size() == 2 && RScevs.size() == 1) |
| RScevs.push_back(RScevs[0]); |
| else if (RScevs.size() == 2 && LScevs.size() == 1) |
| LScevs.push_back(LScevs[0]); |
| else { |
| ScevList.emplace_back(Scev, NeedsFreeze); |
| break; |
| } |
| |
| ScevList.emplace_back( |
| GetBinOpExpr(Opcode, get<0>(LScevs[0]), get<0>(RScevs[0])), |
| NeedsFreeze); |
| ScevList.emplace_back( |
| GetBinOpExpr(Opcode, get<0>(LScevs[1]), get<0>(RScevs[1])), |
| NeedsFreeze); |
| break; |
| } |
| default: |
| // Just return the current SCEV if we haven't handled the instruction yet. |
| LLVM_DEBUG(dbgs() << "ForkedPtr unhandled instruction: " << *I << "\n"); |
| ScevList.emplace_back(Scev, !isGuaranteedNotToBeUndefOrPoison(Ptr)); |
| break; |
| } |
| } |
| |
| static SmallVector<PointerIntPair<const SCEV *, 1, bool>> |
| findForkedPointer(PredicatedScalarEvolution &PSE, |
| const ValueToValueMap &StridesMap, Value *Ptr, |
| const Loop *L) { |
| ScalarEvolution *SE = PSE.getSE(); |
| assert(SE->isSCEVable(Ptr->getType()) && "Value is not SCEVable!"); |
| SmallVector<PointerIntPair<const SCEV *, 1, bool>> Scevs; |
| findForkedSCEVs(SE, L, Ptr, Scevs, MaxForkedSCEVDepth); |
| |
| // For now, we will only accept a forked pointer with two possible SCEVs |
| // that are either SCEVAddRecExprs or loop invariant. |
| if (Scevs.size() == 2 && |
| (isa<SCEVAddRecExpr>(get<0>(Scevs[0])) || |
| SE->isLoopInvariant(get<0>(Scevs[0]), L)) && |
| (isa<SCEVAddRecExpr>(get<0>(Scevs[1])) || |
| SE->isLoopInvariant(get<0>(Scevs[1]), L))) { |
| LLVM_DEBUG(dbgs() << "LAA: Found forked pointer: " << *Ptr << "\n"); |
| LLVM_DEBUG(dbgs() << "\t(1) " << *get<0>(Scevs[0]) << "\n"); |
| LLVM_DEBUG(dbgs() << "\t(2) " << *get<0>(Scevs[1]) << "\n"); |
| return Scevs; |
| } |
| |
| return {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}}; |
| } |
| |
| bool AccessAnalysis::createCheckForAccess(RuntimePointerChecking &RtCheck, |
| MemAccessInfo Access, Type *AccessTy, |
| const ValueToValueMap &StridesMap, |
| DenseMap<Value *, unsigned> &DepSetId, |
| Loop *TheLoop, unsigned &RunningDepId, |
| unsigned ASId, bool ShouldCheckWrap, |
| bool Assume) { |
| Value *Ptr = Access.getPointer(); |
| |
| SmallVector<PointerIntPair<const SCEV *, 1, bool>> TranslatedPtrs = |
| findForkedPointer(PSE, StridesMap, Ptr, TheLoop); |
| |
| for (auto &P : TranslatedPtrs) { |
| const SCEV *PtrExpr = get<0>(P); |
| if (!hasComputableBounds(PSE, Ptr, PtrExpr, TheLoop, Assume)) |
| return false; |
| |
| // When we run after a failing dependency check we have to make sure |
| // we don't have wrapping pointers. |
| if (ShouldCheckWrap) { |
| // Skip wrap checking when translating pointers. |
| if (TranslatedPtrs.size() > 1) |
| return false; |
| |
| if (!isNoWrap(PSE, StridesMap, Ptr, AccessTy, TheLoop)) { |
| auto *Expr = PSE.getSCEV(Ptr); |
| if (!Assume || !isa<SCEVAddRecExpr>(Expr)) |
| return false; |
| PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW); |
| } |
| } |
| // If there's only one option for Ptr, look it up after bounds and wrap |
| // checking, because assumptions might have been added to PSE. |
| if (TranslatedPtrs.size() == 1) |
| TranslatedPtrs[0] = {replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), |
| false}; |
| } |
| |
| for (auto [PtrExpr, NeedsFreeze] : TranslatedPtrs) { |
| // The id of the dependence set. |
| unsigned DepId; |
| |
| if (isDependencyCheckNeeded()) { |
| 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++; |
| |
| bool IsWrite = Access.getInt(); |
| RtCheck.insert(TheLoop, Ptr, PtrExpr, AccessTy, IsWrite, DepId, ASId, PSE, |
| NeedsFreeze); |
| LLVM_DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n'); |
| } |
| |
| return true; |
| } |
| |
| bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck, |
| ScalarEvolution *SE, Loop *TheLoop, |
| const ValueToValueMap &StridesMap, |
| Value *&UncomputablePtr, bool ShouldCheckWrap) { |
| // Find pointers with computable bounds. We are going to use this information |
| // to place a runtime bound check. |
| bool CanDoRT = true; |
| |
| bool MayNeedRTCheck = false; |
| if (!IsRTCheckAnalysisNeeded) return true; |
| |
| bool IsDepCheckNeeded = isDependencyCheckNeeded(); |
| |
| // We assign a consecutive id to access from different alias sets. |
| // Accesses between different groups doesn't need to be checked. |
| unsigned ASId = 0; |
| for (auto &AS : AST) { |
| int NumReadPtrChecks = 0; |
| int NumWritePtrChecks = 0; |
| bool CanDoAliasSetRT = true; |
| ++ASId; |
| |
| // 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; |
| |
| SmallVector<std::pair<MemAccessInfo, Type *>, 4> Retries; |
| |
| // First, count how many write and read accesses are in the alias set. Also |
| // collect MemAccessInfos for later. |
| SmallVector<MemAccessInfo, 4> AccessInfos; |
| for (const auto &A : AS) { |
| Value *Ptr = A.getValue(); |
| bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true)); |
| |
| if (IsWrite) |
| ++NumWritePtrChecks; |
| else |
| ++NumReadPtrChecks; |
| AccessInfos.emplace_back(Ptr, IsWrite); |
| } |
| |
| // We do not need runtime checks for this alias set, if there are no writes |
| // or a single write and no reads. |
| if (NumWritePtrChecks == 0 || |
| (NumWritePtrChecks == 1 && NumReadPtrChecks == 0)) { |
| assert((AS.size() <= 1 || |
| all_of(AS, |
| [this](auto AC) { |
| MemAccessInfo AccessWrite(AC.getValue(), true); |
| return DepCands.findValue(AccessWrite) == DepCands.end(); |
| })) && |
| "Can only skip updating CanDoRT below, if all entries in AS " |
| "are reads or there is at most 1 entry"); |
| continue; |
| } |
| |
| for (auto &Access : AccessInfos) { |
| for (const auto &AccessTy : Accesses[Access]) { |
| if (!createCheckForAccess(RtCheck, Access, AccessTy, StridesMap, |
| DepSetId, TheLoop, RunningDepId, ASId, |
| ShouldCheckWrap, false)) { |
| LLVM_DEBUG(dbgs() << "LAA: Can't find bounds for ptr:" |
| << *Access.getPointer() << '\n'); |
| Retries.push_back({Access, AccessTy}); |
| CanDoAliasSetRT = false; |
| } |
| } |
| } |
| |
| // Note that this function computes CanDoRT and MayNeedRTCheck |
| // independently. For example CanDoRT=false, MayNeedRTCheck=false means that |
| // we have a pointer for which we couldn't find the bounds but we don't |
| // actually need to emit any checks so it does not matter. |
| // |
| // We need runtime checks for this alias set, if there are at least 2 |
| // dependence sets (in which case RunningDepId > 2) or if we need to re-try |
| // any bound checks (because in that case the number of dependence sets is |
| // incomplete). |
| bool NeedsAliasSetRTCheck = RunningDepId > 2 || !Retries.empty(); |
| |
| // We need to perform run-time alias checks, but some pointers had bounds |
| // that couldn't be checked. |
| if (NeedsAliasSetRTCheck && !CanDoAliasSetRT) { |
| // Reset the CanDoSetRt flag and retry all accesses that have failed. |
| // We know that we need these checks, so we can now be more aggressive |
| // and add further checks if required (overflow checks). |
| CanDoAliasSetRT = true; |
| for (auto Retry : Retries) { |
| MemAccessInfo Access = Retry.first; |
| Type *AccessTy = Retry.second; |
| if (!createCheckForAccess(RtCheck, Access, AccessTy, StridesMap, |
| DepSetId, TheLoop, RunningDepId, ASId, |
| ShouldCheckWrap, /*Assume=*/true)) { |
| CanDoAliasSetRT = false; |
| UncomputablePtr = Access.getPointer(); |
| break; |
| } |
| } |
| } |
| |
| CanDoRT &= CanDoAliasSetRT; |
| MayNeedRTCheck |= NeedsAliasSetRTCheck; |
| ++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.Pointers[i].DependencySetId == |
| RtCheck.Pointers[j].DependencySetId) |
| continue; |
| // Only need to check pointers in the same alias set. |
| if (RtCheck.Pointers[i].AliasSetId != RtCheck.Pointers[j].AliasSetId) |
| continue; |
| |
| Value *PtrI = RtCheck.Pointers[i].PointerValue; |
| Value *PtrJ = RtCheck.Pointers[j].PointerValue; |
| |
| unsigned ASi = PtrI->getType()->getPointerAddressSpace(); |
| unsigned ASj = PtrJ->getType()->getPointerAddressSpace(); |
| if (ASi != ASj) { |
| LLVM_DEBUG( |
| dbgs() << "LAA: Runtime check would require comparison between" |
| " different address spaces\n"); |
| return false; |
| } |
| } |
| } |
| |
| if (MayNeedRTCheck && CanDoRT) |
| RtCheck.generateChecks(DepCands, IsDepCheckNeeded); |
| |
| LLVM_DEBUG(dbgs() << "LAA: We need to do " << RtCheck.getNumberOfChecks() |
| << " pointer comparisons.\n"); |
| |
| // If we can do run-time checks, but there are no checks, no runtime checks |
| // are needed. This can happen when all pointers point to the same underlying |
| // object for example. |
| RtCheck.Need = CanDoRT ? RtCheck.getNumberOfChecks() != 0 : MayNeedRTCheck; |
| |
| bool CanDoRTIfNeeded = !RtCheck.Need || CanDoRT; |
| if (!CanDoRTIfNeeded) |
| RtCheck.reset(); |
| return CanDoRTIfNeeded; |
| } |
| |
| 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. |
| |
| LLVM_DEBUG(dbgs() << "LAA: Processing memory accesses...\n"); |
| LLVM_DEBUG(dbgs() << " AST: "; AST.dump()); |
| LLVM_DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\n"); |
| LLVM_DEBUG({ |
| for (auto A : Accesses) |
| dbgs() << "\t" << *A.first.getPointer() << " (" |
| << (A.first.getInt() |
| ? "write" |
| : (ReadOnlyPtr.count(A.first.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 (const 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<const Value*, MemAccessInfo> UnderlyingObjToAccessMap; |
| UnderlyingObjToAccessMap ObjToLastAccess; |
| |
| // Set of access to check after all writes have been processed. |
| PtrAccessMap 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; |
| PtrAccessMap &S = UseDeferred ? DeferredAccesses : Accesses; |
| |
| for (const 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 (const auto &AC : S) { |
| if (AC.first.getPointer() != Ptr) |
| continue; |
| |
| bool IsWrite = AC.first.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) { |
| // We only use the pointer keys, the types vector values don't |
| // matter. |
| 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.push_back(Access); |
| IsRTCheckAnalysisNeeded = true; |
| } |
| |
| if (IsWrite) |
| SetHasWrite = true; |
| |
| // Create sets of pointers connected by a shared alias set and |
| // underlying object. |
| typedef SmallVector<const Value *, 16> ValueVector; |
| ValueVector TempObjects; |
| |
| getUnderlyingObjects(Ptr, TempObjects, LI); |
| LLVM_DEBUG(dbgs() |
| << "Underlying objects for pointer " << *Ptr << "\n"); |
| for (const Value *UnderlyingObj : TempObjects) { |
| // nullptr never alias, don't join sets for pointer that have "null" |
| // in their UnderlyingObjects list. |
| if (isa<ConstantPointerNull>(UnderlyingObj) && |
| !NullPointerIsDefined( |
| TheLoop->getHeader()->getParent(), |
| UnderlyingObj->getType()->getPointerAddressSpace())) |
| continue; |
| |
| UnderlyingObjToAccessMap::iterator Prev = |
| ObjToLastAccess.find(UnderlyingObj); |
| if (Prev != ObjToLastAccess.end()) |
| DepCands.unionSets(Access, Prev->second); |
| |
| ObjToLastAccess[UnderlyingObj] = Access; |
| LLVM_DEBUG(dbgs() << " " << *UnderlyingObj << "\n"); |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| static bool isInBoundsGep(Value *Ptr) { |
| if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) |
| return GEP->isInBounds(); |
| return false; |
| } |
| |
| /// Return true if an AddRec pointer \p Ptr is unsigned non-wrapping, |
| /// i.e. monotonically increasing/decreasing. |
| static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR, |
| PredicatedScalarEvolution &PSE, const Loop *L) { |
| // FIXME: This should probably only return true for NUW. |
| if (AR->getNoWrapFlags(SCEV::NoWrapMask)) |
| return true; |
| |
| // Scalar evolution does not propagate the non-wrapping flags to values that |
| // are derived from a non-wrapping induction variable because non-wrapping |
| // could be flow-sensitive. |
| // |
| // Look through the potentially overflowing instruction to try to prove |
| // non-wrapping for the *specific* value of Ptr. |
| |
| // The arithmetic implied by an inbounds GEP can't overflow. |
| auto *GEP = dyn_cast<GetElementPtrInst>(Ptr); |
| if (!GEP || !GEP->isInBounds()) |
| return false; |
| |
| // Make sure there is only one non-const index and analyze that. |
| Value *NonConstIndex = nullptr; |
| for (Value *Index : GEP->indices()) |
| if (!isa<ConstantInt>(Index)) { |
| if (NonConstIndex) |
| return false; |
| NonConstIndex = Index; |
| } |
| if (!NonConstIndex) |
| // The recurrence is on the pointer, ignore for now. |
| return false; |
| |
| // The index in GEP is signed. It is non-wrapping if it's derived from a NSW |
| // AddRec using a NSW operation. |
| if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(NonConstIndex)) |
| if (OBO->hasNoSignedWrap() && |
| // Assume constant for other the operand so that the AddRec can be |
| // easily found. |
| isa<ConstantInt>(OBO->getOperand(1))) { |
| auto *OpScev = PSE.getSCEV(OBO->getOperand(0)); |
| |
| if (auto *OpAR = dyn_cast<SCEVAddRecExpr>(OpScev)) |
| return OpAR->getLoop() == L && OpAR->getNoWrapFlags(SCEV::FlagNSW); |
| } |
| |
| return false; |
| } |
| |
| /// Check whether the access through \p Ptr has a constant stride. |
| std::optional<int64_t> llvm::getPtrStride(PredicatedScalarEvolution &PSE, |
| Type *AccessTy, Value *Ptr, |
| const Loop *Lp, |
| const ValueToValueMap &StridesMap, |
| bool Assume, bool ShouldCheckWrap) { |
| Type *Ty = Ptr->getType(); |
| assert(Ty->isPointerTy() && "Unexpected non-ptr"); |
| |
| if (isa<ScalableVectorType>(AccessTy)) { |
| LLVM_DEBUG(dbgs() << "LAA: Bad stride - Scalable object: " << *AccessTy |
| << "\n"); |
| return std::nullopt; |
| } |
| |
| const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr); |
| |
| const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); |
| if (Assume && !AR) |
| AR = PSE.getAsAddRec(Ptr); |
| |
| if (!AR) { |
| LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer " << *Ptr |
| << " SCEV: " << *PtrScev << "\n"); |
| return std::nullopt; |
| } |
| |
| // The access function must stride over the innermost loop. |
| if (Lp != AR->getLoop()) { |
| LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop " |
| << *Ptr << " SCEV: " << *AR << "\n"); |
| return std::nullopt; |
| } |
| |
| // 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. |
| unsigned AddrSpace = Ty->getPointerAddressSpace(); |
| bool IsInBoundsGEP = isInBoundsGep(Ptr); |
| bool IsNoWrapAddRec = !ShouldCheckWrap || |
| PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW) || |
| isNoWrapAddRec(Ptr, AR, PSE, Lp); |
| if (!IsNoWrapAddRec && !IsInBoundsGEP && |
| NullPointerIsDefined(Lp->getHeader()->getParent(), AddrSpace)) { |
| if (Assume) { |
| PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW); |
| IsNoWrapAddRec = true; |
| LLVM_DEBUG(dbgs() << "LAA: Pointer may wrap in the address space:\n" |
| << "LAA: Pointer: " << *Ptr << "\n" |
| << "LAA: SCEV: " << *AR << "\n" |
| << "LAA: Added an overflow assumption\n"); |
| } else { |
| LLVM_DEBUG( |
| dbgs() << "LAA: Bad stride - Pointer may wrap in the address space " |
| << *Ptr << " SCEV: " << *AR << "\n"); |
| return std::nullopt; |
| } |
| } |
| |
| // Check the step is constant. |
| const SCEV *Step = AR->getStepRecurrence(*PSE.getSE()); |
| |
| // Calculate the pointer stride and check if it is constant. |
| const SCEVConstant *C = dyn_cast<SCEVConstant>(Step); |
| if (!C) { |
| LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr |
| << " SCEV: " << *AR << "\n"); |
| return std::nullopt; |
| } |
| |
| auto &DL = Lp->getHeader()->getModule()->getDataLayout(); |
| TypeSize AllocSize = DL.getTypeAllocSize(AccessTy); |
| int64_t Size = AllocSize.getFixedValue(); |
| const APInt &APStepVal = C->getAPInt(); |
| |
| // Huge step value - give up. |
| if (APStepVal.getBitWidth() > 64) |
| return std::nullopt; |
| |
| int64_t StepVal = APStepVal.getSExtValue(); |
| |
| // Strided access. |
| int64_t Stride = StepVal / Size; |
| int64_t Rem = StepVal % Size; |
| if (Rem) |
| return std::nullopt; |
| |
| // 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 && Stride != 1 && Stride != -1 && |
| (IsInBoundsGEP || !NullPointerIsDefined(Lp->getHeader()->getParent(), |
| AddrSpace))) { |
| if (Assume) { |
| // We can avoid this case by adding a run-time check. |
| LLVM_DEBUG(dbgs() << "LAA: Non unit strided pointer which is not either " |
| << "inbounds or in address space 0 may wrap:\n" |
| << "LAA: Pointer: " << *Ptr << "\n" |
| << "LAA: SCEV: " << *AR << "\n" |
| << "LAA: Added an overflow assumption\n"); |
| PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW); |
| } else |
| return std::nullopt; |
| } |
| |
| return Stride; |
| } |
| |
| std::optional<int> llvm::getPointersDiff(Type *ElemTyA, Value *PtrA, |
| Type *ElemTyB, Value *PtrB, |
| const DataLayout &DL, |
| ScalarEvolution &SE, bool StrictCheck, |
| bool CheckType) { |
| assert(PtrA && PtrB && "Expected non-nullptr pointers."); |
| assert(cast<PointerType>(PtrA->getType()) |
| ->isOpaqueOrPointeeTypeMatches(ElemTyA) && "Wrong PtrA type"); |
| assert(cast<PointerType>(PtrB->getType()) |
| ->isOpaqueOrPointeeTypeMatches(ElemTyB) && "Wrong PtrB type"); |
| |
| // Make sure that A and B are different pointers. |
| if (PtrA == PtrB) |
| return 0; |
| |
| // Make sure that the element types are the same if required. |
| if (CheckType && ElemTyA != ElemTyB) |
| return std::nullopt; |
| |
| unsigned ASA = PtrA->getType()->getPointerAddressSpace(); |
| unsigned ASB = PtrB->getType()->getPointerAddressSpace(); |
| |
| // Check that the address spaces match. |
| if (ASA != ASB) |
| return std::nullopt; |
| unsigned IdxWidth = DL.getIndexSizeInBits(ASA); |
| |
| APInt OffsetA(IdxWidth, 0), OffsetB(IdxWidth, 0); |
| Value *PtrA1 = PtrA->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetA); |
| Value *PtrB1 = PtrB->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetB); |
| |
| int Val; |
| if (PtrA1 == PtrB1) { |
| // Retrieve the address space again as pointer stripping now tracks through |
| // `addrspacecast`. |
| ASA = cast<PointerType>(PtrA1->getType())->getAddressSpace(); |
| ASB = cast<PointerType>(PtrB1->getType())->getAddressSpace(); |
| // Check that the address spaces match and that the pointers are valid. |
| if (ASA != ASB) |
| return std::nullopt; |
| |
| IdxWidth = DL.getIndexSizeInBits(ASA); |
| OffsetA = OffsetA.sextOrTrunc(IdxWidth); |
| OffsetB = OffsetB.sextOrTrunc(IdxWidth); |
| |
| OffsetB -= OffsetA; |
| Val = OffsetB.getSExtValue(); |
| } else { |
| // Otherwise compute the distance with SCEV between the base pointers. |
| const SCEV *PtrSCEVA = SE.getSCEV(PtrA); |
| const SCEV *PtrSCEVB = SE.getSCEV(PtrB); |
| const auto *Diff = |
| dyn_cast<SCEVConstant>(SE.getMinusSCEV(PtrSCEVB, PtrSCEVA)); |
| if (!Diff) |
| return std::nullopt; |
| Val = Diff->getAPInt().getSExtValue(); |
| } |
| int Size = DL.getTypeStoreSize(ElemTyA); |
| int Dist = Val / Size; |
| |
| // Ensure that the calculated distance matches the type-based one after all |
| // the bitcasts removal in the provided pointers. |
| if (!StrictCheck || Dist * Size == Val) |
| return Dist; |
| return std::nullopt; |
| } |
| |
| bool llvm::sortPtrAccesses(ArrayRef<Value *> VL, Type *ElemTy, |
| const DataLayout &DL, ScalarEvolution &SE, |
| SmallVectorImpl<unsigned> &SortedIndices) { |
| assert(llvm::all_of( |
| VL, [](const Value *V) { return V->getType()->isPointerTy(); }) && |
| "Expected list of pointer operands."); |
| // Walk over the pointers, and map each of them to an offset relative to |
| // first pointer in the array. |
| Value *Ptr0 = VL[0]; |
| |
| using DistOrdPair = std::pair<int64_t, int>; |
| auto Compare = llvm::less_first(); |
| std::set<DistOrdPair, decltype(Compare)> Offsets(Compare); |
| Offsets.emplace(0, 0); |
| int Cnt = 1; |
| bool IsConsecutive = true; |
| for (auto *Ptr : VL.drop_front()) { |
| std::optional<int> Diff = getPointersDiff(ElemTy, Ptr0, ElemTy, Ptr, DL, SE, |
| /*StrictCheck=*/true); |
| if (!Diff) |
| return false; |
| |
| // Check if the pointer with the same offset is found. |
| int64_t Offset = *Diff; |
| auto Res = Offsets.emplace(Offset, Cnt); |
| if (!Res.second) |
| return false; |
| // Consecutive order if the inserted element is the last one. |
| IsConsecutive = IsConsecutive && std::next(Res.first) == Offsets.end(); |
| ++Cnt; |
| } |
| SortedIndices.clear(); |
| if (!IsConsecutive) { |
| // Fill SortedIndices array only if it is non-consecutive. |
| SortedIndices.resize(VL.size()); |
| Cnt = 0; |
| for (const std::pair<int64_t, int> &Pair : Offsets) { |
| SortedIndices[Cnt] = Pair.second; |
| ++Cnt; |
| } |
| } |
| return true; |
| } |
| |
| /// Returns true if the memory operations \p A and \p B are consecutive. |
| bool llvm::isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL, |
| ScalarEvolution &SE, bool CheckType) { |
| Value *PtrA = getLoadStorePointerOperand(A); |
| Value *PtrB = getLoadStorePointerOperand(B); |
| if (!PtrA || !PtrB) |
| return false; |
| Type *ElemTyA = getLoadStoreType(A); |
| Type *ElemTyB = getLoadStoreType(B); |
| std::optional<int> Diff = |
| getPointersDiff(ElemTyA, PtrA, ElemTyB, PtrB, DL, SE, |
| /*StrictCheck=*/true, CheckType); |
| return Diff && *Diff == 1; |
| } |
| |
| void MemoryDepChecker::addAccess(StoreInst *SI) { |
| visitPointers(SI->getPointerOperand(), *InnermostLoop, |
| [this, SI](Value *Ptr) { |
| Accesses[MemAccessInfo(Ptr, true)].push_back(AccessIdx); |
| InstMap.push_back(SI); |
| ++AccessIdx; |
| }); |
| } |
| |
| void MemoryDepChecker::addAccess(LoadInst *LI) { |
| visitPointers(LI->getPointerOperand(), *InnermostLoop, |
| [this, LI](Value *Ptr) { |
| Accesses[MemAccessInfo(Ptr, false)].push_back(AccessIdx); |
| InstMap.push_back(LI); |
| ++AccessIdx; |
| }); |
| } |
| |
| MemoryDepChecker::VectorizationSafetyStatus |
| MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) { |
| switch (Type) { |
| case NoDep: |
| case Forward: |
| case BackwardVectorizable: |
| return VectorizationSafetyStatus::Safe; |
| |
| case Unknown: |
| return VectorizationSafetyStatus::PossiblySafeWithRtChecks; |
| case ForwardButPreventsForwarding: |
| case Backward: |
| case BackwardVectorizableButPreventsForwarding: |
| return VectorizationSafetyStatus::Unsafe; |
| } |
| llvm_unreachable("unexpected DepType!"); |
| } |
| |
| bool MemoryDepChecker::Dependence::isBackward() const { |
| switch (Type) { |
| case NoDep: |
| case Forward: |
| case ForwardButPreventsForwarding: |
| case Unknown: |
| return false; |
| |
| case BackwardVectorizable: |
| case Backward: |
| case BackwardVectorizableButPreventsForwarding: |
| return true; |
| } |
| llvm_unreachable("unexpected DepType!"); |
| } |
| |
| bool MemoryDepChecker::Dependence::isPossiblyBackward() const { |
| return isBackward() || Type == Unknown; |
| } |
| |
| bool MemoryDepChecker::Dependence::isForward() const { |
| switch (Type) { |
| case Forward: |
| case ForwardButPreventsForwarding: |
| return true; |
| |
| case NoDep: |
| case Unknown: |
| case BackwardVectorizable: |
| case Backward: |
| case BackwardVectorizableButPreventsForwarding: |
| return false; |
| } |
| llvm_unreachable("unexpected DepType!"); |
| } |
| |
| bool MemoryDepChecker::couldPreventStoreLoadForward(uint64_t Distance, |
| uint64_t 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. |
| |
| // After this many iterations store-to-load forwarding conflicts should not |
| // cause any slowdowns. |
| const uint64_t NumItersForStoreLoadThroughMemory = 8 * TypeByteSize; |
| // Maximum vector factor. |
| uint64_t MaxVFWithoutSLForwardIssues = std::min( |
| VectorizerParams::MaxVectorWidth * TypeByteSize, MaxSafeDepDistBytes); |
| |
| // Compute the smallest VF at which the store and load would be misaligned. |
| for (uint64_t VF = 2 * TypeByteSize; VF <= MaxVFWithoutSLForwardIssues; |
| VF *= 2) { |
| // If the number of vector iteration between the store and the load are |
| // small we could incur conflicts. |
| if (Distance % VF && Distance / VF < NumItersForStoreLoadThroughMemory) { |
| MaxVFWithoutSLForwardIssues = (VF >> 1); |
| break; |
| } |
| } |
| |
| if (MaxVFWithoutSLForwardIssues < 2 * TypeByteSize) { |
| LLVM_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; |
| } |
| |
| void MemoryDepChecker::mergeInStatus(VectorizationSafetyStatus S) { |
| if (Status < S) |
| Status = S; |
| } |
| |
| /// Given a dependence-distance \p Dist between two |
| /// memory accesses, that have the same stride whose absolute value is given |
| /// in \p Stride, and that have the same type size \p TypeByteSize, |
| /// in a loop whose takenCount is \p BackedgeTakenCount, check if it is |
| /// possible to prove statically that the dependence distance is larger |
| /// than the range that the accesses will travel through the execution of |
| /// the loop. If so, return true; false otherwise. This is useful for |
| /// example in loops such as the following (PR31098): |
| /// for (i = 0; i < D; ++i) { |
| /// = out[i]; |
| /// out[i+D] = |
| /// } |
| static bool isSafeDependenceDistance(const DataLayout &DL, ScalarEvolution &SE, |
| const SCEV &BackedgeTakenCount, |
| const SCEV &Dist, uint64_t Stride, |
| uint64_t TypeByteSize) { |
| |
| // If we can prove that |
| // (**) |Dist| > BackedgeTakenCount * Step |
| // where Step is the absolute stride of the memory accesses in bytes, |
| // then there is no dependence. |
| // |
| // Rationale: |
| // We basically want to check if the absolute distance (|Dist/Step|) |
| // is >= the loop iteration count (or > BackedgeTakenCount). |
| // This is equivalent to the Strong SIV Test (Practical Dependence Testing, |
| // Section 4.2.1); Note, that for vectorization it is sufficient to prove |
| // that the dependence distance is >= VF; This is checked elsewhere. |
| // But in some cases we can prune dependence distances early, and |
| // even before selecting the VF, and without a runtime test, by comparing |
| // the distance against the loop iteration count. Since the vectorized code |
| // will be executed only if LoopCount >= VF, proving distance >= LoopCount |
| // also guarantees that distance >= VF. |
| // |
| const uint64_t ByteStride = Stride * TypeByteSize; |
| const SCEV *Step = SE.getConstant(BackedgeTakenCount.getType(), ByteStride); |
| const SCEV *Product = SE.getMulExpr(&BackedgeTakenCount, Step); |
| |
| const SCEV *CastedDist = &Dist; |
| const SCEV *CastedProduct = Product; |
| uint64_t DistTypeSizeBits = DL.getTypeSizeInBits(Dist.getType()); |
| uint64_t ProductTypeSizeBits = DL.getTypeSizeInBits(Product->getType()); |
| |
| // The dependence distance can be positive/negative, so we sign extend Dist; |
| // The multiplication of the absolute stride in bytes and the |
| // backedgeTakenCount is non-negative, so we zero extend Product. |
| if (DistTypeSizeBits > ProductTypeSizeBits) |
| CastedProduct = SE.getZeroExtendExpr(Product, Dist.getType()); |
| else |
| CastedDist = SE.getNoopOrSignExtend(&Dist, Product->getType()); |
| |
| // Is Dist - (BackedgeTakenCount * Step) > 0 ? |
| // (If so, then we have proven (**) because |Dist| >= Dist) |
| const SCEV *Minus = SE.getMinusSCEV(CastedDist, CastedProduct); |
| if (SE.isKnownPositive(Minus)) |
| return true; |
| |
| // Second try: Is -Dist - (BackedgeTakenCount * Step) > 0 ? |
| // (If so, then we have proven (**) because |Dist| >= -1*Dist) |
| const SCEV *NegDist = SE.getNegativeSCEV(CastedDist); |
| Minus = SE.getMinusSCEV(NegDist, CastedProduct); |
| if (SE.isKnownPositive(Minus)) |
| return true; |
| |
| return false; |
| } |
| |
| /// Check the dependence for two accesses with the same stride \p Stride. |
| /// \p Distance is the positive distance and \p TypeByteSize is type size in |
| /// bytes. |
| /// |
| /// \returns true if they are independent. |
| static bool areStridedAccessesIndependent(uint64_t Distance, uint64_t Stride, |
| uint64_t TypeByteSize) { |
| assert(Stride > 1 && "The stride must be greater than 1"); |
| assert(TypeByteSize > 0 && "The type size in byte must be non-zero"); |
| assert(Distance > 0 && "The distance must be non-zero"); |
| |
| // Skip if the distance is not multiple of type byte size. |
| if (Distance % TypeByteSize) |
| return false; |
| |
| uint64_t ScaledDist = Distance / TypeByteSize; |
| |
| // No dependence if the scaled distance is not multiple of the stride. |
| // E.g. |
| // for (i = 0; i < 1024 ; i += 4) |
| // A[i+2] = A[i] + 1; |
| // |
| // Two accesses in memory (scaled distance is 2, stride is 4): |
| // | A[0] | | | | A[4] | | | | |
| // | | | A[2] | | | | A[6] | | |
| // |
| // E.g. |
| // for (i = 0; i < 1024 ; i += 3) |
| // A[i+4] = A[i] + 1; |
| // |
| // Two accesses in memory (scaled distance is 4, stride is 3): |
| // | A[0] | | | A[3] | | | A[6] | | | |
| // | | | | | A[4] | | | A[7] | | |
| return ScaledDist % Stride; |
| } |
| |
| 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"); |
| |
| auto [APtr, AIsWrite] = A; |
| auto [BPtr, BIsWrite] = B; |
| Type *ATy = getLoadStoreType(InstMap[AIdx]); |
| Type *BTy = getLoadStoreType(InstMap[BIdx]); |
| |
| // 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; |
| |
| int64_t StrideAPtr = |
| getPtrStride(PSE, ATy, APtr, InnermostLoop, Strides, true).value_or(0); |
| int64_t StrideBPtr = |
| getPtrStride(PSE, BTy, BPtr, InnermostLoop, Strides, true).value_or(0); |
| |
| const SCEV *Src = PSE.getSCEV(APtr); |
| const SCEV *Sink = PSE.getSCEV(BPtr); |
| |
| // If the induction step is negative we have to invert source and sink of the |
| // dependence. |
| if (StrideAPtr < 0) { |
| std::swap(APtr, BPtr); |
| std::swap(ATy, BTy); |
| std::swap(Src, Sink); |
| std::swap(AIsWrite, BIsWrite); |
| std::swap(AIdx, BIdx); |
| std::swap(StrideAPtr, StrideBPtr); |
| } |
| |
| ScalarEvolution &SE = *PSE.getSE(); |
| const SCEV *Dist = SE.getMinusSCEV(Sink, Src); |
| |
| LLVM_DEBUG(dbgs() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sink |
| << "(Induction step: " << StrideAPtr << ")\n"); |
| LLVM_DEBUG(dbgs() << "LAA: Distance for " << *InstMap[AIdx] << " to " |
| << *InstMap[BIdx] << ": " << *Dist << "\n"); |
| |
| // Need accesses with constant stride. 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){ |
| LLVM_DEBUG(dbgs() << "Pointer access with non-constant stride\n"); |
| return Dependence::Unknown; |
| } |
| |
| auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout(); |
| uint64_t TypeByteSize = DL.getTypeAllocSize(ATy); |
| bool HasSameSize = |
| DL.getTypeStoreSizeInBits(ATy) == DL.getTypeStoreSizeInBits(BTy); |
| uint64_t Stride = std::abs(StrideAPtr); |
| |
| if (!isa<SCEVCouldNotCompute>(Dist) && HasSameSize && |
| isSafeDependenceDistance(DL, SE, *(PSE.getBackedgeTakenCount()), *Dist, |
| Stride, TypeByteSize)) |
| return Dependence::NoDep; |
| |
| const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist); |
| if (!C) { |
| LLVM_DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n"); |
| FoundNonConstantDistanceDependence = true; |
| return Dependence::Unknown; |
| } |
| |
| const APInt &Val = C->getAPInt(); |
| int64_t Distance = Val.getSExtValue(); |
| |
| // Attempt to prove strided accesses independent. |
| if (std::abs(Distance) > 0 && Stride > 1 && HasSameSize && |
| areStridedAccessesIndependent(std::abs(Distance), Stride, TypeByteSize)) { |
| LLVM_DEBUG(dbgs() << "LAA: Strided accesses are independent\n"); |
| return Dependence::NoDep; |
| } |
| |
| // Negative distances are not plausible dependencies. |
| if (Val.isNegative()) { |
| bool IsTrueDataDependence = (AIsWrite && !BIsWrite); |
| if (IsTrueDataDependence && EnableForwardingConflictDetection && |
| (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) || |
| !HasSameSize)) { |
| LLVM_DEBUG(dbgs() << "LAA: Forward but may prevent st->ld forwarding\n"); |
| return Dependence::ForwardButPreventsForwarding; |
| } |
| |
| LLVM_DEBUG(dbgs() << "LAA: Dependence is negative\n"); |
| return Dependence::Forward; |
| } |
| |
| // Write to the same location with the same size. |
| if (Val == 0) { |
| if (HasSameSize) |
| return Dependence::Forward; |
| LLVM_DEBUG( |
| dbgs() << "LAA: Zero dependence difference but different type sizes\n"); |
| return Dependence::Unknown; |
| } |
| |
| assert(Val.isStrictlyPositive() && "Expect a positive value"); |
| |
| if (!HasSameSize) { |
| LLVM_DEBUG(dbgs() << "LAA: ReadWrite-Write positive dependency with " |
| "different type sizes\n"); |
| return Dependence::Unknown; |
| } |
| |
| // 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 minimum number of iterations for a vectorized/unrolled version. |
| unsigned MinNumIter = std::max(ForcedFactor * ForcedUnroll, 2U); |
| |
| // It's not vectorizable if the distance is smaller than the minimum distance |
| // needed for a vectroized/unrolled version. Vectorizing one iteration in |
| // front needs TypeByteSize * Stride. Vectorizing the last iteration needs |
| // TypeByteSize (No need to plus the last gap distance). |
| // |
| // E.g. Assume one char is 1 byte in memory and one int is 4 bytes. |
| // foo(int *A) { |
| // int *B = (int *)((char *)A + 14); |
| // for (i = 0 ; i < 1024 ; i += 2) |
| // B[i] = A[i] + 1; |
| // } |
| // |
| // Two accesses in memory (stride is 2): |
| // | A[0] | | A[2] | | A[4] | | A[6] | | |
| // | B[0] | | B[2] | | B[4] | |
| // |
| // Distance needs for vectorizing iterations except the last iteration: |
| // 4 * 2 * (MinNumIter - 1). Distance needs for the last iteration: 4. |
| // So the minimum distance needed is: 4 * 2 * (MinNumIter - 1) + 4. |
| // |
| // If MinNumIter is 2, it is vectorizable as the minimum distance needed is |
| // 12, which is less than distance. |
| // |
| // If MinNumIter is 4 (Say if a user forces the vectorization factor to be 4), |
| // the minimum distance needed is 28, which is greater than distance. It is |
| // not safe to do vectorization. |
| uint64_t MinDistanceNeeded = |
| TypeByteSize * Stride * (MinNumIter - 1) + TypeByteSize; |
| if (MinDistanceNeeded > static_cast<uint64_t>(Distance)) { |
| LLVM_DEBUG(dbgs() << "LAA: Failure because of positive distance " |
| << Distance << '\n'); |
| return Dependence::Backward; |
| } |
| |
| // Unsafe if the minimum distance needed is greater than max safe distance. |
| if (MinDistanceNeeded > MaxSafeDepDistBytes) { |
| LLVM_DEBUG(dbgs() << "LAA: Failure because it needs at least " |
| << MinDistanceNeeded << " size in bytes\n"); |
| return Dependence::Backward; |
| } |
| |
| // Positive distance bigger than max vectorization factor. |
| // FIXME: Should use max factor instead of max distance in bytes, which could |
| // not handle different types. |
| // E.g. Assume one char is 1 byte in memory and one int is 4 bytes. |
| // void foo (int *A, char *B) { |
| // for (unsigned i = 0; i < 1024; i++) { |
| // A[i+2] = A[i] + 1; |
| // B[i+2] = B[i] + 1; |
| // } |
| // } |
| // |
| // This case is currently unsafe according to the max safe distance. If we |
| // analyze the two accesses on array B, the max safe dependence distance |
| // is 2. Then we analyze the accesses on array A, the minimum distance needed |
| // is 8, which is less than 2 and forbidden vectorization, But actually |
| // both A and B could be vectorized by 2 iterations. |
| MaxSafeDepDistBytes = |
| std::min(static_cast<uint64_t>(Distance), MaxSafeDepDistBytes); |
| |
| bool IsTrueDataDependence = (!AIsWrite && BIsWrite); |
| if (IsTrueDataDependence && EnableForwardingConflictDetection && |
| couldPreventStoreLoadForward(Distance, TypeByteSize)) |
| return Dependence::BackwardVectorizableButPreventsForwarding; |
| |
| uint64_t MaxVF = MaxSafeDepDistBytes / (TypeByteSize * Stride); |
| LLVM_DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue() |
| << " with max VF = " << MaxVF << '\n'); |
| uint64_t MaxVFInBits = MaxVF * TypeByteSize * 8; |
| MaxSafeVectorWidthInBits = std::min(MaxSafeVectorWidthInBits, MaxVFInBits); |
| return Dependence::BackwardVectorizable; |
| } |
| |
| bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets, |
| MemAccessInfoList &CheckDeps, |
| const ValueToValueMap &Strides) { |
| |
| MaxSafeDepDistBytes = -1; |
| SmallPtrSet<MemAccessInfo, 8> Visited; |
| for (MemAccessInfo CurAccess : CheckDeps) { |
| if (Visited.count(CurAccess)) |
| continue; |
| |
| // 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 = |
| AccessSets.member_begin(I); |
| EquivalenceClasses<MemAccessInfo>::member_iterator AE = |
| AccessSets.member_end(); |
| |
| // Check every access pair. |
| while (AI != AE) { |
| Visited.insert(*AI); |
| bool AIIsWrite = AI->getInt(); |
| // Check loads only against next equivalent class, but stores also against |
| // other stores in the same equivalence class - to the same address. |
| EquivalenceClasses<MemAccessInfo>::member_iterator OI = |
| (AIIsWrite ? AI : 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) |
| // Scan all accesses of another equivalence class, but only the next |
| // accesses of the same equivalent class. |
| for (std::vector<unsigned>::iterator |
| I2 = (OI == AI ? std::next(I1) : Accesses[*OI].begin()), |
| I2E = (OI == AI ? I1E : 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); |
| mergeInStatus(Dependence::isSafeForVectorization(Type)); |
| |
| // Gather dependences unless we accumulated MaxDependences |
| // dependences. In that case return as soon as we find the first |
| // unsafe dependence. This puts a limit on this quadratic |
| // algorithm. |
| if (RecordDependences) { |
| if (Type != Dependence::NoDep) |
| Dependences.push_back(Dependence(A.second, B.second, Type)); |
| |
| if (Dependences.size() >= MaxDependences) { |
| RecordDependences = false; |
| Dependences.clear(); |
| LLVM_DEBUG(dbgs() |
| << "Too many dependences, stopped recording\n"); |
| } |
| } |
| if (!RecordDependences && !isSafeForVectorization()) |
| return false; |
| } |
| ++OI; |
| } |
| AI++; |
| } |
| } |
| |
| LLVM_DEBUG(dbgs() << "Total Dependences: " << Dependences.size() << "\n"); |
| return isSafeForVectorization(); |
| } |
| |
| SmallVector<Instruction *, 4> |
| MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const { |
| MemAccessInfo Access(Ptr, isWrite); |
| auto &IndexVector = Accesses.find(Access)->second; |
| |
| SmallVector<Instruction *, 4> Insts; |
| transform(IndexVector, |
| 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 need to have a loop header. |
| LLVM_DEBUG(dbgs() << "LAA: Found a loop in " |
| << TheLoop->getHeader()->getParent()->getName() << ": " |
| << TheLoop->getHeader()->getName() << '\n'); |
| |
| // We can only analyze innermost loops. |
| if (!TheLoop->isInnermost()) { |
| LLVM_DEBUG(dbgs() << "LAA: loop is not the innermost loop\n"); |
| recordAnalysis("NotInnerMostLoop") << "loop is not the innermost loop"; |
| return false; |
| } |
| |
| // We must have a single backedge. |
| if (TheLoop->getNumBackEdges() != 1) { |
| LLVM_DEBUG( |
| dbgs() << "LAA: loop control flow is not understood by analyzer\n"); |
| recordAnalysis("CFGNotUnderstood") |
| << "loop control flow is not understood by analyzer"; |
| return false; |
| } |
| |
| // ScalarEvolution needs to be able to find the exit count. |
| const SCEV *ExitCount = PSE->getBackedgeTakenCount(); |
| if (isa<SCEVCouldNotCompute>(ExitCount)) { |
| recordAnalysis("CantComputeNumberOfIterations") |
| << "could not determine number of loop iterations"; |
| LLVM_DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n"); |
| return false; |
| } |
| |
| return true; |
| } |
| |
| void LoopAccessInfo::analyzeLoop(AAResults *AA, LoopInfo *LI, |
| const TargetLibraryInfo *TLI, |
| DominatorTree *DT) { |
| // Holds the Load and Store instructions. |
| SmallVector<LoadInst *, 16> Loads; |
| SmallVector<StoreInst *, 16> Stores; |
| |
| // Holds all the different accesses in the loop. |
| unsigned NumReads = 0; |
| unsigned NumReadWrites = 0; |
| |
| bool HasComplexMemInst = false; |
| |
| // A runtime check is only legal to insert if there are no convergent calls. |
| HasConvergentOp = false; |
| |
| PtrRtChecking->Pointers.clear(); |
| PtrRtChecking->Need = false; |
| |
| const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel(); |
| |
| const bool EnableMemAccessVersioningOfLoop = |
| EnableMemAccessVersioning && |
| !TheLoop->getHeader()->getParent()->hasOptSize(); |
| |
| // Traverse blocks in fixed RPOT order, regardless of their storage in the |
| // loop info, as it may be arbitrary. |
| LoopBlocksRPO RPOT(TheLoop); |
| RPOT.perform(LI); |
| for (BasicBlock *BB : RPOT) { |
| // Scan the BB and collect legal loads and stores. Also detect any |
| // convergent instructions. |
| for (Instruction &I : *BB) { |
| if (auto *Call = dyn_cast<CallBase>(&I)) { |
| if (Call->isConvergent()) |
| HasConvergentOp = true; |
| } |
| |
| // With both a non-vectorizable memory instruction and a convergent |
| // operation, found in this loop, no reason to continue the search. |
| if (HasComplexMemInst && HasConvergentOp) { |
| CanVecMem = false; |
| return; |
| } |
| |
| // Avoid hitting recordAnalysis multiple times. |
| if (HasComplexMemInst) |
| continue; |
| |
| // 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 (I.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. |
| auto *Call = dyn_cast<CallInst>(&I); |
| if (Call && getVectorIntrinsicIDForCall(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() && |
| !VFDatabase::getMappings(*Call).empty()) |
| continue; |
| |
| auto *Ld = dyn_cast<LoadInst>(&I); |
| if (!Ld) { |
| recordAnalysis("CantVectorizeInstruction", Ld) |
| << "instruction cannot be vectorized"; |
| HasComplexMemInst = true; |
| continue; |
| } |
| if (!Ld->isSimple() && !IsAnnotatedParallel) { |
| recordAnalysis("NonSimpleLoad", Ld) |
| << "read with atomic ordering or volatile read"; |
| LLVM_DEBUG(dbgs() << "LAA: Found a non-simple load.\n"); |
| HasComplexMemInst = true; |
| continue; |
| } |
| NumLoads++; |
| Loads.push_back(Ld); |
| DepChecker->addAccess(Ld); |
| if (EnableMemAccessVersioningOfLoop) |
| collectStridedAccess(Ld); |
| continue; |
| } |
| |
| // Save 'store' instructions. Abort if other instructions write to memory. |
| if (I.mayWriteToMemory()) { |
| auto *St = dyn_cast<StoreInst>(&I); |
| if (!St) { |
| recordAnalysis("CantVectorizeInstruction", St) |
| << "instruction cannot be vectorized"; |
| HasComplexMemInst = true; |
| continue; |
| } |
| if (!St->isSimple() && !IsAnnotatedParallel) { |
| recordAnalysis("NonSimpleStore", St) |
| << "write with atomic ordering or volatile write"; |
| LLVM_DEBUG(dbgs() << "LAA: Found a non-simple store.\n"); |
| HasComplexMemInst = true; |
| continue; |
| } |
| NumStores++; |
| Stores.push_back(St); |
| DepChecker->addAccess(St); |
| if (EnableMemAccessVersioningOfLoop) |
| collectStridedAccess(St); |
| } |
| } // Next instr. |
| } // Next block. |
| |
| if (HasComplexMemInst) { |
| CanVecMem = false; |
| return; |
| } |
| |
| // 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()) { |
| LLVM_DEBUG(dbgs() << "LAA: Found a read-only loop!\n"); |
| CanVecMem = true; |
| return; |
| } |
| |
| MemoryDepChecker::DepCandidates DependentAccesses; |
| AccessAnalysis Accesses(TheLoop, AA, LI, DependentAccesses, *PSE); |
| |
| // 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. |
| SmallSet<std::pair<Value *, Type *>, 16> Seen; |
| |
| // Record uniform store addresses to identify if we have multiple stores |
| // to the same address. |
| SmallPtrSet<Value *, 16> UniformStores; |
| |
| for (StoreInst *ST : Stores) { |
| Value *Ptr = ST->getPointerOperand(); |
| |
| if (isUniform(Ptr)) { |
| // Record store instructions to loop invariant addresses |
| StoresToInvariantAddresses.push_back(ST); |
| HasDependenceInvolvingLoopInvariantAddress |= |
| !UniformStores.insert(Ptr).second; |
| } |
| |
| // If we did *not* see this pointer before, insert it to the read-write |
| // list. At this phase it is only a 'write' list. |
| Type *AccessTy = getLoadStoreType(ST); |
| if (Seen.insert({Ptr, AccessTy}).second) { |
| ++NumReadWrites; |
| |
| MemoryLocation Loc = MemoryLocation::get(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; |
| |
| visitPointers(const_cast<Value *>(Loc.Ptr), *TheLoop, |
| [&Accesses, AccessTy, Loc](Value *Ptr) { |
| MemoryLocation NewLoc = Loc.getWithNewPtr(Ptr); |
| Accesses.addStore(NewLoc, AccessTy); |
| }); |
| } |
| } |
| |
| if (IsAnnotatedParallel) { |
| LLVM_DEBUG( |
| dbgs() << "LAA: A loop annotated parallel, ignore memory dependency " |
| << "checks.\n"); |
| CanVecMem = true; |
| return; |
| } |
| |
| for (LoadInst *LD : Loads) { |
| 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; |
| Type *AccessTy = getLoadStoreType(LD); |
| if (Seen.insert({Ptr, AccessTy}).second || |
| !getPtrStride(*PSE, LD->getType(), Ptr, TheLoop, SymbolicStrides).value_or(0)) { |
| ++NumReads; |
| IsReadOnlyPtr = true; |
| } |
| |
| // See if there is an unsafe dependency between a load to a uniform address and |
| // store to the same uniform address. |
| if (UniformStores.count(Ptr)) { |
| LLVM_DEBUG(dbgs() << "LAA: Found an unsafe dependency between a uniform " |
| "load and uniform store to the same address!\n"); |
| HasDependenceInvolvingLoopInvariantAddress = true; |
| } |
| |
| MemoryLocation Loc = MemoryLocation::get(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; |
| |
| visitPointers(const_cast<Value *>(Loc.Ptr), *TheLoop, |
| [&Accesses, AccessTy, Loc, IsReadOnlyPtr](Value *Ptr) { |
| MemoryLocation NewLoc = Loc.getWithNewPtr(Ptr); |
| Accesses.addLoad(NewLoc, AccessTy, 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) { |
| LLVM_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(); |
| |
| // Find pointers with computable bounds. We are going to use this information |
| // to place a runtime bound check. |
| Value *UncomputablePtr = nullptr; |
| bool CanDoRTIfNeeded = |
| Accesses.canCheckPtrAtRT(*PtrRtChecking, PSE->getSE(), TheLoop, |
| SymbolicStrides, UncomputablePtr, false); |
| if (!CanDoRTIfNeeded) { |
| auto *I = dyn_cast_or_null<Instruction>(UncomputablePtr); |
| recordAnalysis("CantIdentifyArrayBounds", I) |
| << "cannot identify array bounds"; |
| LLVM_DEBUG(dbgs() << "LAA: We can't vectorize because we can't find " |
| << "the array bounds.\n"); |
| CanVecMem = false; |
| return; |
| } |
| |
| LLVM_DEBUG( |
| dbgs() << "LAA: May be able to perform a memory runtime check if needed.\n"); |
| |
| CanVecMem = true; |
| if (Accesses.isDependencyCheckNeeded()) { |
| LLVM_DEBUG(dbgs() << "LAA: Checking memory dependencies\n"); |
| CanVecMem = DepChecker->areDepsSafe( |
| DependentAccesses, Accesses.getDependenciesToCheck(), SymbolicStrides); |
| MaxSafeDepDistBytes = DepChecker->getMaxSafeDepDistBytes(); |
| |
| if (!CanVecMem && DepChecker->shouldRetryWithRuntimeCheck()) { |
| LLVM_DEBUG(dbgs() << "LAA: Retrying with memory checks\n"); |
| |
| // Clear the dependency checks. We assume they are not needed. |
| Accesses.resetDepChecks(*DepChecker); |
| |
| PtrRtChecking->reset(); |
| PtrRtChecking->Need = true; |
| |
| auto *SE = PSE->getSE(); |
| UncomputablePtr = nullptr; |
| CanDoRTIfNeeded = Accesses.canCheckPtrAtRT( |
| *PtrRtChecking, SE, TheLoop, SymbolicStrides, UncomputablePtr, true); |
| |
| // Check that we found the bounds for the pointer. |
| if (!CanDoRTIfNeeded) { |
| auto *I = dyn_cast_or_null<Instruction>(UncomputablePtr); |
| recordAnalysis("CantCheckMemDepsAtRunTime", I) |
| << "cannot check memory dependencies at runtime"; |
| LLVM_DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n"); |
| CanVecMem = false; |
| return; |
| } |
| |
| CanVecMem = true; |
| } |
| } |
| |
| if (HasConvergentOp) { |
| recordAnalysis("CantInsertRuntimeCheckWithConvergent") |
| << "cannot add control dependency to convergent operation"; |
| LLVM_DEBUG(dbgs() << "LAA: We can't vectorize because a runtime check " |
| "would be needed with a convergent operation\n"); |
| CanVecMem = false; |
| return; |
| } |
| |
| if (CanVecMem) |
| LLVM_DEBUG( |
| dbgs() << "LAA: No unsafe dependent memory operations in loop. We" |
| << (PtrRtChecking->Need ? "" : " don't") |
| << " need runtime memory checks.\n"); |
| else |
| emitUnsafeDependenceRemark(); |
| } |
| |
| void LoopAccessInfo::emitUnsafeDependenceRemark() { |
| auto Deps = getDepChecker().getDependences(); |
| if (!Deps) |
| return; |
| auto Found = llvm::find_if(*Deps, [](const MemoryDepChecker::Dependence &D) { |
| return MemoryDepChecker::Dependence::isSafeForVectorization(D.Type) != |
| MemoryDepChecker::VectorizationSafetyStatus::Safe; |
| }); |
| if (Found == Deps->end()) |
| return; |
| MemoryDepChecker::Dependence Dep = *Found; |
| |
| LLVM_DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n"); |
| |
| // Emit remark for first unsafe dependence |
| OptimizationRemarkAnalysis &R = |
| recordAnalysis("UnsafeDep", Dep.getDestination(*this)) |
| << "unsafe dependent memory operations in loop. Use " |
| "#pragma loop distribute(enable) to allow loop distribution " |
| "to attempt to isolate the offending operations into a separate " |
| "loop"; |
| |
| switch (Dep.Type) { |
| case MemoryDepChecker::Dependence::NoDep: |
| case MemoryDepChecker::Dependence::Forward: |
| case MemoryDepChecker::Dependence::BackwardVectorizable: |
| llvm_unreachable("Unexpected dependence"); |
| case MemoryDepChecker::Dependence::Backward: |
| R << "\nBackward loop carried data dependence."; |
| break; |
| case MemoryDepChecker::Dependence::ForwardButPreventsForwarding: |
| R << "\nForward loop carried data dependence that prevents " |
| "store-to-load forwarding."; |
| break; |
| case MemoryDepChecker::Dependence::BackwardVectorizableButPreventsForwarding: |
| R << "\nBackward loop carried data dependence that prevents " |
| "store-to-load forwarding."; |
| break; |
| case MemoryDepChecker::Dependence::Unknown: |
| R << "\nUnknown data dependence."; |
| break; |
| } |
| |
| if (Instruction *I = Dep.getSource(*this)) { |
| DebugLoc SourceLoc = I->getDebugLoc(); |
| if (auto *DD = dyn_cast_or_null<Instruction>(getPointerOperand(I))) |
| SourceLoc = DD->getDebugLoc(); |
| if (SourceLoc) |
| R << " Memory location is the same as accessed at " |
| << ore::NV("Location", SourceLoc); |
| } |
| } |
| |
| 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); |
| } |
| |
| OptimizationRemarkAnalysis &LoopAccessInfo::recordAnalysis(StringRef RemarkName, |
| Instruction *I) { |
| assert(!Report && "Multiple reports generated"); |
| |
| Value *CodeRegion = TheLoop->getHeader(); |
| DebugLoc DL = TheLoop->getStartLoc(); |
| |
| if (I) { |
| CodeRegion = I->getParent(); |
| // If there is no debug location attached to the instruction, revert back to |
| // using the loop's. |
| if (I->getDebugLoc()) |
| DL = I->getDebugLoc(); |
| } |
| |
| Report = std::make_unique<OptimizationRemarkAnalysis>(DEBUG_TYPE, RemarkName, DL, |
| CodeRegion); |
| return *Report; |
| } |
| |
| bool LoopAccessInfo::isUniform(Value *V) const { |
| auto *SE = PSE->getSE(); |
| // Since we rely on SCEV for uniformity, if the type is not SCEVable, it is |
| // never considered uniform. |
| // TODO: Is this really what we want? Even without FP SCEV, we may want some |
| // trivially loop-invariant FP values to be considered uniform. |
| if (!SE->isSCEVable(V->getType())) |
| return false; |
| return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop)); |
| } |
| |
| void LoopAccessInfo::collectStridedAccess(Value *MemAccess) { |
| Value *Ptr = getLoadStorePointerOperand(MemAccess); |
| if (!Ptr) |
| return; |
| |
| Value *Stride = getStrideFromPointer(Ptr, PSE->getSE(), TheLoop); |
| if (!Stride) |
| return; |
| |
| LLVM_DEBUG(dbgs() << "LAA: Found a strided access that is a candidate for " |
| "versioning:"); |
| LLVM_DEBUG(dbgs() << " Ptr: " << *Ptr << " Stride: " << *Stride << "\n"); |
| |
| // Avoid adding the "Stride == 1" predicate when we know that |
| // Stride >= Trip-Count. Such a predicate will effectively optimize a single |
| // or zero iteration loop, as Trip-Count <= Stride == 1. |
| // |
| // TODO: We are currently not making a very informed decision on when it is |
| // beneficial to apply stride versioning. It might make more sense that the |
| // users of this analysis (such as the vectorizer) will trigger it, based on |
| // their specific cost considerations; For example, in cases where stride |
| // versioning does not help resolving memory accesses/dependences, the |
| // vectorizer should evaluate the cost of the runtime test, and the benefit |
| // of various possible stride specializations, considering the alternatives |
| // of using gather/scatters (if available). |
| |
| const SCEV *StrideExpr = PSE->getSCEV(Stride); |
| const SCEV *BETakenCount = PSE->getBackedgeTakenCount(); |
| |
| // Match the types so we can compare the stride and the BETakenCount. |
| // The Stride can be positive/negative, so we sign extend Stride; |
| // The backedgeTakenCount is non-negative, so we zero extend BETakenCount. |
| const DataLayout &DL = TheLoop->getHeader()->getModule()->getDataLayout(); |
| uint64_t StrideTypeSizeBits = DL.getTypeSizeInBits(StrideExpr->getType()); |
| uint64_t BETypeSizeBits = DL.getTypeSizeInBits(BETakenCount->getType()); |
| const SCEV *CastedStride = StrideExpr; |
| const SCEV *CastedBECount = BETakenCount; |
| ScalarEvolution *SE = PSE->getSE(); |
| if (BETypeSizeBits >= StrideTypeSizeBits) |
| CastedStride = SE->getNoopOrSignExtend(StrideExpr, BETakenCount->getType()); |
| else |
| CastedBECount = SE->getZeroExtendExpr(BETakenCount, StrideExpr->getType()); |
| const SCEV *StrideMinusBETaken = SE->getMinusSCEV(CastedStride, CastedBECount); |
| // Since TripCount == BackEdgeTakenCount + 1, checking: |
| // "Stride >= TripCount" is equivalent to checking: |
| // Stride - BETakenCount > 0 |
| if (SE->isKnownPositive(StrideMinusBETaken)) { |
| LLVM_DEBUG( |
| dbgs() << "LAA: Stride>=TripCount; No point in versioning as the " |
| "Stride==1 predicate will imply that the loop executes " |
| "at most once.\n"); |
| return; |
| } |
| LLVM_DEBUG(dbgs() << "LAA: Found a strided access that we can version.\n"); |
| |
| SymbolicStrides[Ptr] = Stride; |
| StrideSet.insert(Stride); |
| } |
| |
| LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE, |
| const TargetLibraryInfo *TLI, AAResults *AA, |
| DominatorTree *DT, LoopInfo *LI) |
| : PSE(std::make_unique<PredicatedScalarEvolution>(*SE, *L)), |
| PtrRtChecking(nullptr), |
| DepChecker(std::make_unique<MemoryDepChecker>(*PSE, L)), TheLoop(L) { |
| PtrRtChecking = std::make_unique<RuntimePointerChecking>(*DepChecker, SE); |
| if (canAnalyzeLoop()) { |
| analyzeLoop(AA, LI, TLI, DT); |
| } |
| } |
| |
| void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const { |
| if (CanVecMem) { |
| OS.indent(Depth) << "Memory dependences are safe"; |
| if (MaxSafeDepDistBytes != -1ULL) |
| OS << " with a maximum dependence distance of " << MaxSafeDepDistBytes |
| << " bytes"; |
| if (PtrRtChecking->Need) |
| OS << " with run-time checks"; |
| OS << "\n"; |
| } |
| |
| if (HasConvergentOp) |
| OS.indent(Depth) << "Has convergent operation in loop\n"; |
| |
| if (Report) |
| OS.indent(Depth) << "Report: " << Report->getMsg() << "\n"; |
| |
| if (auto *Dependences = DepChecker->getDependences()) { |
| OS.indent(Depth) << "Dependences:\n"; |
| for (const auto &Dep : *Dependences) { |
| Dep.print(OS, Depth + 2, DepChecker->getMemoryInstructions()); |
| OS << "\n"; |
| } |
| } else |
| OS.indent(Depth) << "Too many dependences, not recorded\n"; |
| |
| // List the pair of accesses need run-time checks to prove independence. |
| PtrRtChecking->print(OS, Depth); |
| OS << "\n"; |
| |
| OS.indent(Depth) << "Non vectorizable stores to invariant address were " |
| << (HasDependenceInvolvingLoopInvariantAddress ? "" : "not ") |
| << "found in loop.\n"; |
| |
| OS.indent(Depth) << "SCEV assumptions:\n"; |
| PSE->getPredicate().print(OS, Depth); |
| |
| OS << "\n"; |
| |
| OS.indent(Depth) << "Expressions re-written:\n"; |
| PSE->print(OS, Depth); |
| } |
| |
| const LoopAccessInfo &LoopAccessInfoManager::getInfo(Loop &L) { |
| auto I = LoopAccessInfoMap.insert({&L, nullptr}); |
| |
| if (I.second) |
| I.first->second = |
| std::make_unique<LoopAccessInfo>(&L, &SE, TLI, &AA, &DT, &LI); |
| |
| return *I.first->second; |
| } |
| |
| LoopAccessLegacyAnalysis::LoopAccessLegacyAnalysis() : FunctionPass(ID) { |
| initializeLoopAccessLegacyAnalysisPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool LoopAccessLegacyAnalysis::runOnFunction(Function &F) { |
| auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE(); |
| auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>(); |
| auto *TLI = TLIP ? &TLIP->getTLI(F) : nullptr; |
| auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults(); |
| auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| LAIs = std::make_unique<LoopAccessInfoManager>(SE, AA, DT, LI, TLI); |
| return false; |
| } |
| |
| void LoopAccessLegacyAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequiredTransitive<ScalarEvolutionWrapperPass>(); |
| AU.addRequiredTransitive<AAResultsWrapperPass>(); |
| AU.addRequiredTransitive<DominatorTreeWrapperPass>(); |
| AU.addRequiredTransitive<LoopInfoWrapperPass>(); |
| |
| AU.setPreservesAll(); |
| } |
| |
| LoopAccessInfoManager LoopAccessAnalysis::run(Function &F, |
| FunctionAnalysisManager &AM) { |
| return LoopAccessInfoManager( |
| AM.getResult<ScalarEvolutionAnalysis>(F), AM.getResult<AAManager>(F), |
| AM.getResult<DominatorTreeAnalysis>(F), AM.getResult<LoopAnalysis>(F), |
| &AM.getResult<TargetLibraryAnalysis>(F)); |
| } |
| |
| char LoopAccessLegacyAnalysis::ID = 0; |
| static const char laa_name[] = "Loop Access Analysis"; |
| #define LAA_NAME "loop-accesses" |
| |
| INITIALIZE_PASS_BEGIN(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true) |
| INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) |
| INITIALIZE_PASS_END(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true) |
| |
| AnalysisKey LoopAccessAnalysis::Key; |
| |
| namespace llvm { |
| |
| Pass *createLAAPass() { |
| return new LoopAccessLegacyAnalysis(); |
| } |
| |
| } // end namespace llvm |