| //===- Loads.cpp - Local load analysis ------------------------------------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines simple local analyses for load instructions. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/Loads.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/AssumeBundleQueries.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/MemoryBuiltins.h" |
| #include "llvm/Analysis/MemoryLocation.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/Analysis/ScalarEvolutionExpressions.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/Operator.h" |
| |
| using namespace llvm; |
| |
| static bool isAligned(const Value *Base, const APInt &Offset, Align Alignment, |
| const DataLayout &DL) { |
| Align BA = Base->getPointerAlignment(DL); |
| const APInt APAlign(Offset.getBitWidth(), Alignment.value()); |
| assert(APAlign.isPowerOf2() && "must be a power of 2!"); |
| return BA >= Alignment && !(Offset & (APAlign - 1)); |
| } |
| |
| /// Test if V is always a pointer to allocated and suitably aligned memory for |
| /// a simple load or store. |
| static bool isDereferenceableAndAlignedPointer( |
| const Value *V, Align Alignment, const APInt &Size, const DataLayout &DL, |
| const Instruction *CtxI, AssumptionCache *AC, const DominatorTree *DT, |
| const TargetLibraryInfo *TLI, SmallPtrSetImpl<const Value *> &Visited, |
| unsigned MaxDepth) { |
| assert(V->getType()->isPointerTy() && "Base must be pointer"); |
| |
| // Recursion limit. |
| if (MaxDepth-- == 0) |
| return false; |
| |
| // Already visited? Bail out, we've likely hit unreachable code. |
| if (!Visited.insert(V).second) |
| return false; |
| |
| // Note that it is not safe to speculate into a malloc'd region because |
| // malloc may return null. |
| |
| // For GEPs, determine if the indexing lands within the allocated object. |
| if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) { |
| const Value *Base = GEP->getPointerOperand(); |
| |
| APInt Offset(DL.getIndexTypeSizeInBits(GEP->getType()), 0); |
| if (!GEP->accumulateConstantOffset(DL, Offset) || Offset.isNegative() || |
| !Offset.urem(APInt(Offset.getBitWidth(), Alignment.value())) |
| .isMinValue()) |
| return false; |
| |
| // If the base pointer is dereferenceable for Offset+Size bytes, then the |
| // GEP (== Base + Offset) is dereferenceable for Size bytes. If the base |
| // pointer is aligned to Align bytes, and the Offset is divisible by Align |
| // then the GEP (== Base + Offset == k_0 * Align + k_1 * Align) is also |
| // aligned to Align bytes. |
| |
| // Offset and Size may have different bit widths if we have visited an |
| // addrspacecast, so we can't do arithmetic directly on the APInt values. |
| return isDereferenceableAndAlignedPointer( |
| Base, Alignment, Offset + Size.sextOrTrunc(Offset.getBitWidth()), DL, |
| CtxI, AC, DT, TLI, Visited, MaxDepth); |
| } |
| |
| // bitcast instructions are no-ops as far as dereferenceability is concerned. |
| if (const BitCastOperator *BC = dyn_cast<BitCastOperator>(V)) { |
| if (BC->getSrcTy()->isPointerTy()) |
| return isDereferenceableAndAlignedPointer( |
| BC->getOperand(0), Alignment, Size, DL, CtxI, AC, DT, TLI, |
| Visited, MaxDepth); |
| } |
| |
| // Recurse into both hands of select. |
| if (const SelectInst *Sel = dyn_cast<SelectInst>(V)) { |
| return isDereferenceableAndAlignedPointer(Sel->getTrueValue(), Alignment, |
| Size, DL, CtxI, AC, DT, TLI, |
| Visited, MaxDepth) && |
| isDereferenceableAndAlignedPointer(Sel->getFalseValue(), Alignment, |
| Size, DL, CtxI, AC, DT, TLI, |
| Visited, MaxDepth); |
| } |
| |
| bool CheckForNonNull, CheckForFreed; |
| APInt KnownDerefBytes(Size.getBitWidth(), |
| V->getPointerDereferenceableBytes(DL, CheckForNonNull, |
| CheckForFreed)); |
| if (KnownDerefBytes.getBoolValue() && KnownDerefBytes.uge(Size) && |
| !CheckForFreed) |
| if (!CheckForNonNull || isKnownNonZero(V, DL, 0, AC, CtxI, DT)) { |
| // As we recursed through GEPs to get here, we've incrementally checked |
| // that each step advanced by a multiple of the alignment. If our base is |
| // properly aligned, then the original offset accessed must also be. |
| APInt Offset(DL.getTypeStoreSizeInBits(V->getType()), 0); |
| return isAligned(V, Offset, Alignment, DL); |
| } |
| |
| /// TODO refactor this function to be able to search independently for |
| /// Dereferencability and Alignment requirements. |
| |
| |
| if (const auto *Call = dyn_cast<CallBase>(V)) { |
| if (auto *RP = getArgumentAliasingToReturnedPointer(Call, true)) |
| return isDereferenceableAndAlignedPointer(RP, Alignment, Size, DL, CtxI, |
| AC, DT, TLI, Visited, MaxDepth); |
| |
| // If we have a call we can't recurse through, check to see if this is an |
| // allocation function for which we can establish an minimum object size. |
| // Such a minimum object size is analogous to a deref_or_null attribute in |
| // that we still need to prove the result non-null at point of use. |
| // NOTE: We can only use the object size as a base fact as we a) need to |
| // prove alignment too, and b) don't want the compile time impact of a |
| // separate recursive walk. |
| ObjectSizeOpts Opts; |
| // TODO: It may be okay to round to align, but that would imply that |
| // accessing slightly out of bounds was legal, and we're currently |
| // inconsistent about that. For the moment, be conservative. |
| Opts.RoundToAlign = false; |
| Opts.NullIsUnknownSize = true; |
| uint64_t ObjSize; |
| if (getObjectSize(V, ObjSize, DL, TLI, Opts)) { |
| APInt KnownDerefBytes(Size.getBitWidth(), ObjSize); |
| if (KnownDerefBytes.getBoolValue() && KnownDerefBytes.uge(Size) && |
| isKnownNonZero(V, DL, 0, AC, CtxI, DT) && !V->canBeFreed()) { |
| // As we recursed through GEPs to get here, we've incrementally |
| // checked that each step advanced by a multiple of the alignment. If |
| // our base is properly aligned, then the original offset accessed |
| // must also be. |
| APInt Offset(DL.getTypeStoreSizeInBits(V->getType()), 0); |
| return isAligned(V, Offset, Alignment, DL); |
| } |
| } |
| } |
| |
| // For gc.relocate, look through relocations |
| if (const GCRelocateInst *RelocateInst = dyn_cast<GCRelocateInst>(V)) |
| return isDereferenceableAndAlignedPointer(RelocateInst->getDerivedPtr(), |
| Alignment, Size, DL, CtxI, AC, DT, |
| TLI, Visited, MaxDepth); |
| |
| if (const AddrSpaceCastOperator *ASC = dyn_cast<AddrSpaceCastOperator>(V)) |
| return isDereferenceableAndAlignedPointer(ASC->getOperand(0), Alignment, |
| Size, DL, CtxI, AC, DT, TLI, |
| Visited, MaxDepth); |
| |
| if (CtxI) { |
| /// Look through assumes to see if both dereferencability and alignment can |
| /// be provent by an assume |
| RetainedKnowledge AlignRK; |
| RetainedKnowledge DerefRK; |
| if (getKnowledgeForValue( |
| V, {Attribute::Dereferenceable, Attribute::Alignment}, AC, |
| [&](RetainedKnowledge RK, Instruction *Assume, auto) { |
| if (!isValidAssumeForContext(Assume, CtxI)) |
| return false; |
| if (RK.AttrKind == Attribute::Alignment) |
| AlignRK = std::max(AlignRK, RK); |
| if (RK.AttrKind == Attribute::Dereferenceable) |
| DerefRK = std::max(DerefRK, RK); |
| if (AlignRK && DerefRK && AlignRK.ArgValue >= Alignment.value() && |
| DerefRK.ArgValue >= Size.getZExtValue()) |
| return true; // We have found what we needed so we stop looking |
| return false; // Other assumes may have better information. so |
| // keep looking |
| })) |
| return true; |
| } |
| |
| // If we don't know, assume the worst. |
| return false; |
| } |
| |
| bool llvm::isDereferenceableAndAlignedPointer( |
| const Value *V, Align Alignment, const APInt &Size, const DataLayout &DL, |
| const Instruction *CtxI, AssumptionCache *AC, const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| // Note: At the moment, Size can be zero. This ends up being interpreted as |
| // a query of whether [Base, V] is dereferenceable and V is aligned (since |
| // that's what the implementation happened to do). It's unclear if this is |
| // the desired semantic, but at least SelectionDAG does exercise this case. |
| |
| SmallPtrSet<const Value *, 32> Visited; |
| return ::isDereferenceableAndAlignedPointer(V, Alignment, Size, DL, CtxI, AC, |
| DT, TLI, Visited, 16); |
| } |
| |
| bool llvm::isDereferenceableAndAlignedPointer( |
| const Value *V, Type *Ty, Align Alignment, const DataLayout &DL, |
| const Instruction *CtxI, AssumptionCache *AC, const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| // For unsized types or scalable vectors we don't know exactly how many bytes |
| // are dereferenced, so bail out. |
| if (!Ty->isSized() || isa<ScalableVectorType>(Ty)) |
| return false; |
| |
| // When dereferenceability information is provided by a dereferenceable |
| // attribute, we know exactly how many bytes are dereferenceable. If we can |
| // determine the exact offset to the attributed variable, we can use that |
| // information here. |
| |
| APInt AccessSize(DL.getPointerTypeSizeInBits(V->getType()), |
| DL.getTypeStoreSize(Ty)); |
| return isDereferenceableAndAlignedPointer(V, Alignment, AccessSize, DL, CtxI, |
| AC, DT, TLI); |
| } |
| |
| bool llvm::isDereferenceablePointer(const Value *V, Type *Ty, |
| const DataLayout &DL, |
| const Instruction *CtxI, |
| AssumptionCache *AC, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| return isDereferenceableAndAlignedPointer(V, Ty, Align(1), DL, CtxI, AC, DT, |
| TLI); |
| } |
| |
| /// Test if A and B will obviously have the same value. |
| /// |
| /// This includes recognizing that %t0 and %t1 will have the same |
| /// value in code like this: |
| /// \code |
| /// %t0 = getelementptr \@a, 0, 3 |
| /// store i32 0, i32* %t0 |
| /// %t1 = getelementptr \@a, 0, 3 |
| /// %t2 = load i32* %t1 |
| /// \endcode |
| /// |
| static bool AreEquivalentAddressValues(const Value *A, const Value *B) { |
| // Test if the values are trivially equivalent. |
| if (A == B) |
| return true; |
| |
| // Test if the values come from identical arithmetic instructions. |
| // Use isIdenticalToWhenDefined instead of isIdenticalTo because |
| // this function is only used when one address use dominates the |
| // other, which means that they'll always either have the same |
| // value or one of them will have an undefined value. |
| if (isa<BinaryOperator>(A) || isa<CastInst>(A) || isa<PHINode>(A) || |
| isa<GetElementPtrInst>(A)) |
| if (const Instruction *BI = dyn_cast<Instruction>(B)) |
| if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI)) |
| return true; |
| |
| // Otherwise they may not be equivalent. |
| return false; |
| } |
| |
| bool llvm::isDereferenceableAndAlignedInLoop(LoadInst *LI, Loop *L, |
| ScalarEvolution &SE, |
| DominatorTree &DT, |
| AssumptionCache *AC) { |
| auto &DL = LI->getModule()->getDataLayout(); |
| Value *Ptr = LI->getPointerOperand(); |
| |
| APInt EltSize(DL.getIndexTypeSizeInBits(Ptr->getType()), |
| DL.getTypeStoreSize(LI->getType()).getFixedValue()); |
| const Align Alignment = LI->getAlign(); |
| |
| Instruction *HeaderFirstNonPHI = L->getHeader()->getFirstNonPHI(); |
| |
| // If given a uniform (i.e. non-varying) address, see if we can prove the |
| // access is safe within the loop w/o needing predication. |
| if (L->isLoopInvariant(Ptr)) |
| return isDereferenceableAndAlignedPointer(Ptr, Alignment, EltSize, DL, |
| HeaderFirstNonPHI, AC, &DT); |
| |
| // Otherwise, check to see if we have a repeating access pattern where we can |
| // prove that all accesses are well aligned and dereferenceable. |
| auto *AddRec = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(Ptr)); |
| if (!AddRec || AddRec->getLoop() != L || !AddRec->isAffine()) |
| return false; |
| auto* Step = dyn_cast<SCEVConstant>(AddRec->getStepRecurrence(SE)); |
| if (!Step) |
| return false; |
| // TODO: generalize to access patterns which have gaps |
| if (Step->getAPInt() != EltSize) |
| return false; |
| |
| auto TC = SE.getSmallConstantMaxTripCount(L); |
| if (!TC) |
| return false; |
| |
| const APInt AccessSize = TC * EltSize; |
| |
| auto *StartS = dyn_cast<SCEVUnknown>(AddRec->getStart()); |
| if (!StartS) |
| return false; |
| assert(SE.isLoopInvariant(StartS, L) && "implied by addrec definition"); |
| Value *Base = StartS->getValue(); |
| |
| // For the moment, restrict ourselves to the case where the access size is a |
| // multiple of the requested alignment and the base is aligned. |
| // TODO: generalize if a case found which warrants |
| if (EltSize.urem(Alignment.value()) != 0) |
| return false; |
| return isDereferenceableAndAlignedPointer(Base, Alignment, AccessSize, DL, |
| HeaderFirstNonPHI, AC, &DT); |
| } |
| |
| /// Check if executing a load of this pointer value cannot trap. |
| /// |
| /// If DT and ScanFrom are specified this method performs context-sensitive |
| /// analysis and returns true if it is safe to load immediately before ScanFrom. |
| /// |
| /// If it is not obviously safe to load from the specified pointer, we do |
| /// a quick local scan of the basic block containing \c ScanFrom, to determine |
| /// if the address is already accessed. |
| /// |
| /// This uses the pointee type to determine how many bytes need to be safe to |
| /// load from the pointer. |
| bool llvm::isSafeToLoadUnconditionally(Value *V, Align Alignment, APInt &Size, |
| const DataLayout &DL, |
| Instruction *ScanFrom, |
| AssumptionCache *AC, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| // If DT is not specified we can't make context-sensitive query |
| const Instruction* CtxI = DT ? ScanFrom : nullptr; |
| if (isDereferenceableAndAlignedPointer(V, Alignment, Size, DL, CtxI, AC, DT, |
| TLI)) |
| return true; |
| |
| if (!ScanFrom) |
| return false; |
| |
| if (Size.getBitWidth() > 64) |
| return false; |
| const uint64_t LoadSize = Size.getZExtValue(); |
| |
| // Otherwise, be a little bit aggressive by scanning the local block where we |
| // want to check to see if the pointer is already being loaded or stored |
| // from/to. If so, the previous load or store would have already trapped, |
| // so there is no harm doing an extra load (also, CSE will later eliminate |
| // the load entirely). |
| BasicBlock::iterator BBI = ScanFrom->getIterator(), |
| E = ScanFrom->getParent()->begin(); |
| |
| // We can at least always strip pointer casts even though we can't use the |
| // base here. |
| V = V->stripPointerCasts(); |
| |
| while (BBI != E) { |
| --BBI; |
| |
| // If we see a free or a call which may write to memory (i.e. which might do |
| // a free) the pointer could be marked invalid. |
| if (isa<CallInst>(BBI) && BBI->mayWriteToMemory() && |
| !isa<LifetimeIntrinsic>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) |
| return false; |
| |
| Value *AccessedPtr; |
| Type *AccessedTy; |
| Align AccessedAlign; |
| if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { |
| // Ignore volatile loads. The execution of a volatile load cannot |
| // be used to prove an address is backed by regular memory; it can, |
| // for example, point to an MMIO register. |
| if (LI->isVolatile()) |
| continue; |
| AccessedPtr = LI->getPointerOperand(); |
| AccessedTy = LI->getType(); |
| AccessedAlign = LI->getAlign(); |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) { |
| // Ignore volatile stores (see comment for loads). |
| if (SI->isVolatile()) |
| continue; |
| AccessedPtr = SI->getPointerOperand(); |
| AccessedTy = SI->getValueOperand()->getType(); |
| AccessedAlign = SI->getAlign(); |
| } else |
| continue; |
| |
| if (AccessedAlign < Alignment) |
| continue; |
| |
| // Handle trivial cases. |
| if (AccessedPtr == V && |
| LoadSize <= DL.getTypeStoreSize(AccessedTy)) |
| return true; |
| |
| if (AreEquivalentAddressValues(AccessedPtr->stripPointerCasts(), V) && |
| LoadSize <= DL.getTypeStoreSize(AccessedTy)) |
| return true; |
| } |
| return false; |
| } |
| |
| bool llvm::isSafeToLoadUnconditionally(Value *V, Type *Ty, Align Alignment, |
| const DataLayout &DL, |
| Instruction *ScanFrom, |
| AssumptionCache *AC, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| TypeSize TySize = DL.getTypeStoreSize(Ty); |
| if (TySize.isScalable()) |
| return false; |
| APInt Size(DL.getIndexTypeSizeInBits(V->getType()), TySize.getFixedValue()); |
| return isSafeToLoadUnconditionally(V, Alignment, Size, DL, ScanFrom, AC, DT, |
| TLI); |
| } |
| |
| /// DefMaxInstsToScan - the default number of maximum instructions |
| /// to scan in the block, used by FindAvailableLoadedValue(). |
| /// FindAvailableLoadedValue() was introduced in r60148, to improve jump |
| /// threading in part by eliminating partially redundant loads. |
| /// At that point, the value of MaxInstsToScan was already set to '6' |
| /// without documented explanation. |
| cl::opt<unsigned> |
| llvm::DefMaxInstsToScan("available-load-scan-limit", cl::init(6), cl::Hidden, |
| cl::desc("Use this to specify the default maximum number of instructions " |
| "to scan backward from a given instruction, when searching for " |
| "available loaded value")); |
| |
| Value *llvm::FindAvailableLoadedValue(LoadInst *Load, |
| BasicBlock *ScanBB, |
| BasicBlock::iterator &ScanFrom, |
| unsigned MaxInstsToScan, |
| AAResults *AA, bool *IsLoad, |
| unsigned *NumScanedInst) { |
| // Don't CSE load that is volatile or anything stronger than unordered. |
| if (!Load->isUnordered()) |
| return nullptr; |
| |
| MemoryLocation Loc = MemoryLocation::get(Load); |
| return findAvailablePtrLoadStore(Loc, Load->getType(), Load->isAtomic(), |
| ScanBB, ScanFrom, MaxInstsToScan, AA, IsLoad, |
| NumScanedInst); |
| } |
| |
| // Check if the load and the store have the same base, constant offsets and |
| // non-overlapping access ranges. |
| static bool areNonOverlapSameBaseLoadAndStore(const Value *LoadPtr, |
| Type *LoadTy, |
| const Value *StorePtr, |
| Type *StoreTy, |
| const DataLayout &DL) { |
| APInt LoadOffset(DL.getIndexTypeSizeInBits(LoadPtr->getType()), 0); |
| APInt StoreOffset(DL.getIndexTypeSizeInBits(StorePtr->getType()), 0); |
| const Value *LoadBase = LoadPtr->stripAndAccumulateConstantOffsets( |
| DL, LoadOffset, /* AllowNonInbounds */ false); |
| const Value *StoreBase = StorePtr->stripAndAccumulateConstantOffsets( |
| DL, StoreOffset, /* AllowNonInbounds */ false); |
| if (LoadBase != StoreBase) |
| return false; |
| auto LoadAccessSize = LocationSize::precise(DL.getTypeStoreSize(LoadTy)); |
| auto StoreAccessSize = LocationSize::precise(DL.getTypeStoreSize(StoreTy)); |
| ConstantRange LoadRange(LoadOffset, |
| LoadOffset + LoadAccessSize.toRaw()); |
| ConstantRange StoreRange(StoreOffset, |
| StoreOffset + StoreAccessSize.toRaw()); |
| return LoadRange.intersectWith(StoreRange).isEmptySet(); |
| } |
| |
| static Value *getAvailableLoadStore(Instruction *Inst, const Value *Ptr, |
| Type *AccessTy, bool AtLeastAtomic, |
| const DataLayout &DL, bool *IsLoadCSE) { |
| // If this is a load of Ptr, the loaded value is available. |
| // (This is true even if the load is volatile or atomic, although |
| // those cases are unlikely.) |
| if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { |
| // We can value forward from an atomic to a non-atomic, but not the |
| // other way around. |
| if (LI->isAtomic() < AtLeastAtomic) |
| return nullptr; |
| |
| Value *LoadPtr = LI->getPointerOperand()->stripPointerCasts(); |
| if (!AreEquivalentAddressValues(LoadPtr, Ptr)) |
| return nullptr; |
| |
| if (CastInst::isBitOrNoopPointerCastable(LI->getType(), AccessTy, DL)) { |
| if (IsLoadCSE) |
| *IsLoadCSE = true; |
| return LI; |
| } |
| } |
| |
| // If this is a store through Ptr, the value is available! |
| // (This is true even if the store is volatile or atomic, although |
| // those cases are unlikely.) |
| if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { |
| // We can value forward from an atomic to a non-atomic, but not the |
| // other way around. |
| if (SI->isAtomic() < AtLeastAtomic) |
| return nullptr; |
| |
| Value *StorePtr = SI->getPointerOperand()->stripPointerCasts(); |
| if (!AreEquivalentAddressValues(StorePtr, Ptr)) |
| return nullptr; |
| |
| if (IsLoadCSE) |
| *IsLoadCSE = false; |
| |
| Value *Val = SI->getValueOperand(); |
| if (CastInst::isBitOrNoopPointerCastable(Val->getType(), AccessTy, DL)) |
| return Val; |
| |
| TypeSize StoreSize = DL.getTypeSizeInBits(Val->getType()); |
| TypeSize LoadSize = DL.getTypeSizeInBits(AccessTy); |
| if (TypeSize::isKnownLE(LoadSize, StoreSize)) |
| if (auto *C = dyn_cast<Constant>(Val)) |
| return ConstantFoldLoadFromConst(C, AccessTy, DL); |
| } |
| |
| if (auto *MSI = dyn_cast<MemSetInst>(Inst)) { |
| // Don't forward from (non-atomic) memset to atomic load. |
| if (AtLeastAtomic) |
| return nullptr; |
| |
| // Only handle constant memsets. |
| auto *Val = dyn_cast<ConstantInt>(MSI->getValue()); |
| auto *Len = dyn_cast<ConstantInt>(MSI->getLength()); |
| if (!Val || !Len) |
| return nullptr; |
| |
| // TODO: Handle offsets. |
| Value *Dst = MSI->getDest(); |
| if (!AreEquivalentAddressValues(Dst, Ptr)) |
| return nullptr; |
| |
| if (IsLoadCSE) |
| *IsLoadCSE = false; |
| |
| TypeSize LoadTypeSize = DL.getTypeSizeInBits(AccessTy); |
| if (LoadTypeSize.isScalable()) |
| return nullptr; |
| |
| // Make sure the read bytes are contained in the memset. |
| uint64_t LoadSize = LoadTypeSize.getFixedValue(); |
| if ((Len->getValue() * 8).ult(LoadSize)) |
| return nullptr; |
| |
| APInt Splat = LoadSize >= 8 ? APInt::getSplat(LoadSize, Val->getValue()) |
| : Val->getValue().trunc(LoadSize); |
| ConstantInt *SplatC = ConstantInt::get(MSI->getContext(), Splat); |
| if (CastInst::isBitOrNoopPointerCastable(SplatC->getType(), AccessTy, DL)) |
| return SplatC; |
| |
| return nullptr; |
| } |
| |
| return nullptr; |
| } |
| |
| Value *llvm::findAvailablePtrLoadStore( |
| const MemoryLocation &Loc, Type *AccessTy, bool AtLeastAtomic, |
| BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan, |
| AAResults *AA, bool *IsLoadCSE, unsigned *NumScanedInst) { |
| if (MaxInstsToScan == 0) |
| MaxInstsToScan = ~0U; |
| |
| const DataLayout &DL = ScanBB->getModule()->getDataLayout(); |
| const Value *StrippedPtr = Loc.Ptr->stripPointerCasts(); |
| |
| while (ScanFrom != ScanBB->begin()) { |
| // We must ignore debug info directives when counting (otherwise they |
| // would affect codegen). |
| Instruction *Inst = &*--ScanFrom; |
| if (Inst->isDebugOrPseudoInst()) |
| continue; |
| |
| // Restore ScanFrom to expected value in case next test succeeds |
| ScanFrom++; |
| |
| if (NumScanedInst) |
| ++(*NumScanedInst); |
| |
| // Don't scan huge blocks. |
| if (MaxInstsToScan-- == 0) |
| return nullptr; |
| |
| --ScanFrom; |
| |
| if (Value *Available = getAvailableLoadStore(Inst, StrippedPtr, AccessTy, |
| AtLeastAtomic, DL, IsLoadCSE)) |
| return Available; |
| |
| // Try to get the store size for the type. |
| if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { |
| Value *StorePtr = SI->getPointerOperand()->stripPointerCasts(); |
| |
| // If both StrippedPtr and StorePtr reach all the way to an alloca or |
| // global and they are different, ignore the store. This is a trivial form |
| // of alias analysis that is important for reg2mem'd code. |
| if ((isa<AllocaInst>(StrippedPtr) || isa<GlobalVariable>(StrippedPtr)) && |
| (isa<AllocaInst>(StorePtr) || isa<GlobalVariable>(StorePtr)) && |
| StrippedPtr != StorePtr) |
| continue; |
| |
| if (!AA) { |
| // When AA isn't available, but if the load and the store have the same |
| // base, constant offsets and non-overlapping access ranges, ignore the |
| // store. This is a simple form of alias analysis that is used by the |
| // inliner. FIXME: use BasicAA if possible. |
| if (areNonOverlapSameBaseLoadAndStore( |
| Loc.Ptr, AccessTy, SI->getPointerOperand(), |
| SI->getValueOperand()->getType(), DL)) |
| continue; |
| } else { |
| // If we have alias analysis and it says the store won't modify the |
| // loaded value, ignore the store. |
| if (!isModSet(AA->getModRefInfo(SI, Loc))) |
| continue; |
| } |
| |
| // Otherwise the store that may or may not alias the pointer, bail out. |
| ++ScanFrom; |
| return nullptr; |
| } |
| |
| // If this is some other instruction that may clobber Ptr, bail out. |
| if (Inst->mayWriteToMemory()) { |
| // If alias analysis claims that it really won't modify the load, |
| // ignore it. |
| if (AA && !isModSet(AA->getModRefInfo(Inst, Loc))) |
| continue; |
| |
| // May modify the pointer, bail out. |
| ++ScanFrom; |
| return nullptr; |
| } |
| } |
| |
| // Got to the start of the block, we didn't find it, but are done for this |
| // block. |
| return nullptr; |
| } |
| |
| Value *llvm::FindAvailableLoadedValue(LoadInst *Load, AAResults &AA, |
| bool *IsLoadCSE, |
| unsigned MaxInstsToScan) { |
| const DataLayout &DL = Load->getModule()->getDataLayout(); |
| Value *StrippedPtr = Load->getPointerOperand()->stripPointerCasts(); |
| BasicBlock *ScanBB = Load->getParent(); |
| Type *AccessTy = Load->getType(); |
| bool AtLeastAtomic = Load->isAtomic(); |
| |
| if (!Load->isUnordered()) |
| return nullptr; |
| |
| // Try to find an available value first, and delay expensive alias analysis |
| // queries until later. |
| Value *Available = nullptr;; |
| SmallVector<Instruction *> MustNotAliasInsts; |
| for (Instruction &Inst : make_range(++Load->getReverseIterator(), |
| ScanBB->rend())) { |
| if (Inst.isDebugOrPseudoInst()) |
| continue; |
| |
| if (MaxInstsToScan-- == 0) |
| return nullptr; |
| |
| Available = getAvailableLoadStore(&Inst, StrippedPtr, AccessTy, |
| AtLeastAtomic, DL, IsLoadCSE); |
| if (Available) |
| break; |
| |
| if (Inst.mayWriteToMemory()) |
| MustNotAliasInsts.push_back(&Inst); |
| } |
| |
| // If we found an available value, ensure that the instructions in between |
| // did not modify the memory location. |
| if (Available) { |
| MemoryLocation Loc = MemoryLocation::get(Load); |
| for (Instruction *Inst : MustNotAliasInsts) |
| if (isModSet(AA.getModRefInfo(Inst, Loc))) |
| return nullptr; |
| } |
| |
| return Available; |
| } |
| |
| bool llvm::canReplacePointersIfEqual(Value *A, Value *B, const DataLayout &DL, |
| Instruction *CtxI) { |
| Type *Ty = A->getType(); |
| assert(Ty == B->getType() && Ty->isPointerTy() && |
| "values must have matching pointer types"); |
| |
| // NOTE: The checks in the function are incomplete and currently miss illegal |
| // cases! The current implementation is a starting point and the |
| // implementation should be made stricter over time. |
| if (auto *C = dyn_cast<Constant>(B)) { |
| // Do not allow replacing a pointer with a constant pointer, unless it is |
| // either null or at least one byte is dereferenceable. |
| APInt OneByte(DL.getPointerTypeSizeInBits(Ty), 1); |
| return C->isNullValue() || |
| isDereferenceableAndAlignedPointer(B, Align(1), OneByte, DL, CtxI); |
| } |
| |
| return true; |
| } |
