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Diffstat (limited to 'llvm/lib/Analysis/BasicAliasAnalysis.cpp')
| -rw-r--r-- | llvm/lib/Analysis/BasicAliasAnalysis.cpp | 2100 |
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diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp new file mode 100644 index 000000000000..f3c30c258c19 --- /dev/null +++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp @@ -0,0 +1,2100 @@ +//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===// +// +// 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 the primary stateless implementation of the +// Alias Analysis interface that implements identities (two different +// globals cannot alias, etc), but does no stateful analysis. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Analysis/BasicAliasAnalysis.h" +#include "llvm/ADT/APInt.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/Analysis/CaptureTracking.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/MemoryLocation.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/Analysis/PhiValues.h" +#include "llvm/IR/Argument.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/Constant.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GetElementPtrTypeIterator.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Operator.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/KnownBits.h" +#include <cassert> +#include <cstdint> +#include <cstdlib> +#include <utility> + +#define DEBUG_TYPE "basicaa" + +using namespace llvm; + +/// Enable analysis of recursive PHI nodes. +static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", cl::Hidden, + cl::init(false)); + +/// By default, even on 32-bit architectures we use 64-bit integers for +/// calculations. This will allow us to more-aggressively decompose indexing +/// expressions calculated using i64 values (e.g., long long in C) which is +/// common enough to worry about. +static cl::opt<bool> ForceAtLeast64Bits("basicaa-force-at-least-64b", + cl::Hidden, cl::init(true)); +static cl::opt<bool> DoubleCalcBits("basicaa-double-calc-bits", + cl::Hidden, cl::init(false)); + +/// SearchLimitReached / SearchTimes shows how often the limit of +/// to decompose GEPs is reached. It will affect the precision +/// of basic alias analysis. +STATISTIC(SearchLimitReached, "Number of times the limit to " + "decompose GEPs is reached"); +STATISTIC(SearchTimes, "Number of times a GEP is decomposed"); + +/// Cutoff after which to stop analysing a set of phi nodes potentially involved +/// in a cycle. Because we are analysing 'through' phi nodes, we need to be +/// careful with value equivalence. We use reachability to make sure a value +/// cannot be involved in a cycle. +const unsigned MaxNumPhiBBsValueReachabilityCheck = 20; + +// The max limit of the search depth in DecomposeGEPExpression() and +// GetUnderlyingObject(), both functions need to use the same search +// depth otherwise the algorithm in aliasGEP will assert. +static const unsigned MaxLookupSearchDepth = 6; + +bool BasicAAResult::invalidate(Function &Fn, const PreservedAnalyses &PA, + FunctionAnalysisManager::Invalidator &Inv) { + // We don't care if this analysis itself is preserved, it has no state. But + // we need to check that the analyses it depends on have been. Note that we + // may be created without handles to some analyses and in that case don't + // depend on them. + if (Inv.invalidate<AssumptionAnalysis>(Fn, PA) || + (DT && Inv.invalidate<DominatorTreeAnalysis>(Fn, PA)) || + (LI && Inv.invalidate<LoopAnalysis>(Fn, PA)) || + (PV && Inv.invalidate<PhiValuesAnalysis>(Fn, PA))) + return true; + + // Otherwise this analysis result remains valid. + return false; +} + +//===----------------------------------------------------------------------===// +// Useful predicates +//===----------------------------------------------------------------------===// + +/// Returns true if the pointer is to a function-local object that never +/// escapes from the function. +static bool isNonEscapingLocalObject( + const Value *V, + SmallDenseMap<const Value *, bool, 8> *IsCapturedCache = nullptr) { + SmallDenseMap<const Value *, bool, 8>::iterator CacheIt; + if (IsCapturedCache) { + bool Inserted; + std::tie(CacheIt, Inserted) = IsCapturedCache->insert({V, false}); + if (!Inserted) + // Found cached result, return it! + return CacheIt->second; + } + + // If this is a local allocation, check to see if it escapes. + if (isa<AllocaInst>(V) || isNoAliasCall(V)) { + // Set StoreCaptures to True so that we can assume in our callers that the + // pointer is not the result of a load instruction. Currently + // PointerMayBeCaptured doesn't have any special analysis for the + // StoreCaptures=false case; if it did, our callers could be refined to be + // more precise. + auto Ret = !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); + if (IsCapturedCache) + CacheIt->second = Ret; + return Ret; + } + + // If this is an argument that corresponds to a byval or noalias argument, + // then it has not escaped before entering the function. Check if it escapes + // inside the function. + if (const Argument *A = dyn_cast<Argument>(V)) + if (A->hasByValAttr() || A->hasNoAliasAttr()) { + // Note even if the argument is marked nocapture, we still need to check + // for copies made inside the function. The nocapture attribute only + // specifies that there are no copies made that outlive the function. + auto Ret = !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); + if (IsCapturedCache) + CacheIt->second = Ret; + return Ret; + } + + return false; +} + +/// Returns true if the pointer is one which would have been considered an +/// escape by isNonEscapingLocalObject. +static bool isEscapeSource(const Value *V) { + if (isa<CallBase>(V)) + return true; + + if (isa<Argument>(V)) + return true; + + // The load case works because isNonEscapingLocalObject considers all + // stores to be escapes (it passes true for the StoreCaptures argument + // to PointerMayBeCaptured). + if (isa<LoadInst>(V)) + return true; + + return false; +} + +/// Returns the size of the object specified by V or UnknownSize if unknown. +static uint64_t getObjectSize(const Value *V, const DataLayout &DL, + const TargetLibraryInfo &TLI, + bool NullIsValidLoc, + bool RoundToAlign = false) { + uint64_t Size; + ObjectSizeOpts Opts; + Opts.RoundToAlign = RoundToAlign; + Opts.NullIsUnknownSize = NullIsValidLoc; + if (getObjectSize(V, Size, DL, &TLI, Opts)) + return Size; + return MemoryLocation::UnknownSize; +} + +/// Returns true if we can prove that the object specified by V is smaller than +/// Size. +static bool isObjectSmallerThan(const Value *V, uint64_t Size, + const DataLayout &DL, + const TargetLibraryInfo &TLI, + bool NullIsValidLoc) { + // Note that the meanings of the "object" are slightly different in the + // following contexts: + // c1: llvm::getObjectSize() + // c2: llvm.objectsize() intrinsic + // c3: isObjectSmallerThan() + // c1 and c2 share the same meaning; however, the meaning of "object" in c3 + // refers to the "entire object". + // + // Consider this example: + // char *p = (char*)malloc(100) + // char *q = p+80; + // + // In the context of c1 and c2, the "object" pointed by q refers to the + // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20. + // + // However, in the context of c3, the "object" refers to the chunk of memory + // being allocated. So, the "object" has 100 bytes, and q points to the middle + // the "object". In case q is passed to isObjectSmallerThan() as the 1st + // parameter, before the llvm::getObjectSize() is called to get the size of + // entire object, we should: + // - either rewind the pointer q to the base-address of the object in + // question (in this case rewind to p), or + // - just give up. It is up to caller to make sure the pointer is pointing + // to the base address the object. + // + // We go for 2nd option for simplicity. + if (!isIdentifiedObject(V)) + return false; + + // This function needs to use the aligned object size because we allow + // reads a bit past the end given sufficient alignment. + uint64_t ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc, + /*RoundToAlign*/ true); + + return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size; +} + +/// Return the minimal extent from \p V to the end of the underlying object, +/// assuming the result is used in an aliasing query. E.g., we do use the query +/// location size and the fact that null pointers cannot alias here. +static uint64_t getMinimalExtentFrom(const Value &V, + const LocationSize &LocSize, + const DataLayout &DL, + bool NullIsValidLoc) { + // If we have dereferenceability information we know a lower bound for the + // extent as accesses for a lower offset would be valid. We need to exclude + // the "or null" part if null is a valid pointer. + bool CanBeNull; + uint64_t DerefBytes = V.getPointerDereferenceableBytes(DL, CanBeNull); + DerefBytes = (CanBeNull && NullIsValidLoc) ? 0 : DerefBytes; + // If queried with a precise location size, we assume that location size to be + // accessed, thus valid. + if (LocSize.isPrecise()) + DerefBytes = std::max(DerefBytes, LocSize.getValue()); + return DerefBytes; +} + +/// Returns true if we can prove that the object specified by V has size Size. +static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL, + const TargetLibraryInfo &TLI, bool NullIsValidLoc) { + uint64_t ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc); + return ObjectSize != MemoryLocation::UnknownSize && ObjectSize == Size; +} + +//===----------------------------------------------------------------------===// +// GetElementPtr Instruction Decomposition and Analysis +//===----------------------------------------------------------------------===// + +/// Analyzes the specified value as a linear expression: "A*V + B", where A and +/// B are constant integers. +/// +/// Returns the scale and offset values as APInts and return V as a Value*, and +/// return whether we looked through any sign or zero extends. The incoming +/// Value is known to have IntegerType, and it may already be sign or zero +/// extended. +/// +/// Note that this looks through extends, so the high bits may not be +/// represented in the result. +/*static*/ const Value *BasicAAResult::GetLinearExpression( + const Value *V, APInt &Scale, APInt &Offset, unsigned &ZExtBits, + unsigned &SExtBits, const DataLayout &DL, unsigned Depth, + AssumptionCache *AC, DominatorTree *DT, bool &NSW, bool &NUW) { + assert(V->getType()->isIntegerTy() && "Not an integer value"); + + // Limit our recursion depth. + if (Depth == 6) { + Scale = 1; + Offset = 0; + return V; + } + + if (const ConstantInt *Const = dyn_cast<ConstantInt>(V)) { + // If it's a constant, just convert it to an offset and remove the variable. + // If we've been called recursively, the Offset bit width will be greater + // than the constant's (the Offset's always as wide as the outermost call), + // so we'll zext here and process any extension in the isa<SExtInst> & + // isa<ZExtInst> cases below. + Offset += Const->getValue().zextOrSelf(Offset.getBitWidth()); + assert(Scale == 0 && "Constant values don't have a scale"); + return V; + } + + if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) { + if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) { + // If we've been called recursively, then Offset and Scale will be wider + // than the BOp operands. We'll always zext it here as we'll process sign + // extensions below (see the isa<SExtInst> / isa<ZExtInst> cases). + APInt RHS = RHSC->getValue().zextOrSelf(Offset.getBitWidth()); + + switch (BOp->getOpcode()) { + default: + // We don't understand this instruction, so we can't decompose it any + // further. + Scale = 1; + Offset = 0; + return V; + case Instruction::Or: + // X|C == X+C if all the bits in C are unset in X. Otherwise we can't + // analyze it. + if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC, + BOp, DT)) { + Scale = 1; + Offset = 0; + return V; + } + LLVM_FALLTHROUGH; + case Instruction::Add: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + Offset += RHS; + break; + case Instruction::Sub: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + Offset -= RHS; + break; + case Instruction::Mul: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + Offset *= RHS; + Scale *= RHS; + break; + case Instruction::Shl: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + + // We're trying to linearize an expression of the kind: + // shl i8 -128, 36 + // where the shift count exceeds the bitwidth of the type. + // We can't decompose this further (the expression would return + // a poison value). + if (Offset.getBitWidth() < RHS.getLimitedValue() || + Scale.getBitWidth() < RHS.getLimitedValue()) { + Scale = 1; + Offset = 0; + return V; + } + + Offset <<= RHS.getLimitedValue(); + Scale <<= RHS.getLimitedValue(); + // the semantics of nsw and nuw for left shifts don't match those of + // multiplications, so we won't propagate them. + NSW = NUW = false; + return V; + } + + if (isa<OverflowingBinaryOperator>(BOp)) { + NUW &= BOp->hasNoUnsignedWrap(); + NSW &= BOp->hasNoSignedWrap(); + } + return V; + } + } + + // Since GEP indices are sign extended anyway, we don't care about the high + // bits of a sign or zero extended value - just scales and offsets. The + // extensions have to be consistent though. + if (isa<SExtInst>(V) || isa<ZExtInst>(V)) { + Value *CastOp = cast<CastInst>(V)->getOperand(0); + unsigned NewWidth = V->getType()->getPrimitiveSizeInBits(); + unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits(); + unsigned OldZExtBits = ZExtBits, OldSExtBits = SExtBits; + const Value *Result = + GetLinearExpression(CastOp, Scale, Offset, ZExtBits, SExtBits, DL, + Depth + 1, AC, DT, NSW, NUW); + + // zext(zext(%x)) == zext(%x), and similarly for sext; we'll handle this + // by just incrementing the number of bits we've extended by. + unsigned ExtendedBy = NewWidth - SmallWidth; + + if (isa<SExtInst>(V) && ZExtBits == 0) { + // sext(sext(%x, a), b) == sext(%x, a + b) + + if (NSW) { + // We haven't sign-wrapped, so it's valid to decompose sext(%x + c) + // into sext(%x) + sext(c). We'll sext the Offset ourselves: + unsigned OldWidth = Offset.getBitWidth(); + Offset = Offset.trunc(SmallWidth).sext(NewWidth).zextOrSelf(OldWidth); + } else { + // We may have signed-wrapped, so don't decompose sext(%x + c) into + // sext(%x) + sext(c) + Scale = 1; + Offset = 0; + Result = CastOp; + ZExtBits = OldZExtBits; + SExtBits = OldSExtBits; + } + SExtBits += ExtendedBy; + } else { + // sext(zext(%x, a), b) = zext(zext(%x, a), b) = zext(%x, a + b) + + if (!NUW) { + // We may have unsigned-wrapped, so don't decompose zext(%x + c) into + // zext(%x) + zext(c) + Scale = 1; + Offset = 0; + Result = CastOp; + ZExtBits = OldZExtBits; + SExtBits = OldSExtBits; + } + ZExtBits += ExtendedBy; + } + + return Result; + } + + Scale = 1; + Offset = 0; + return V; +} + +/// To ensure a pointer offset fits in an integer of size PointerSize +/// (in bits) when that size is smaller than the maximum pointer size. This is +/// an issue, for example, in particular for 32b pointers with negative indices +/// that rely on two's complement wrap-arounds for precise alias information +/// where the maximum pointer size is 64b. +static APInt adjustToPointerSize(APInt Offset, unsigned PointerSize) { + assert(PointerSize <= Offset.getBitWidth() && "Invalid PointerSize!"); + unsigned ShiftBits = Offset.getBitWidth() - PointerSize; + return (Offset << ShiftBits).ashr(ShiftBits); +} + +static unsigned getMaxPointerSize(const DataLayout &DL) { + unsigned MaxPointerSize = DL.getMaxPointerSizeInBits(); + if (MaxPointerSize < 64 && ForceAtLeast64Bits) MaxPointerSize = 64; + if (DoubleCalcBits) MaxPointerSize *= 2; + + return MaxPointerSize; +} + +/// If V is a symbolic pointer expression, decompose it into a base pointer +/// with a constant offset and a number of scaled symbolic offsets. +/// +/// The scaled symbolic offsets (represented by pairs of a Value* and a scale +/// in the VarIndices vector) are Value*'s that are known to be scaled by the +/// specified amount, but which may have other unrepresented high bits. As +/// such, the gep cannot necessarily be reconstructed from its decomposed form. +/// +/// When DataLayout is around, this function is capable of analyzing everything +/// that GetUnderlyingObject can look through. To be able to do that +/// GetUnderlyingObject and DecomposeGEPExpression must use the same search +/// depth (MaxLookupSearchDepth). When DataLayout not is around, it just looks +/// through pointer casts. +bool BasicAAResult::DecomposeGEPExpression(const Value *V, + DecomposedGEP &Decomposed, const DataLayout &DL, AssumptionCache *AC, + DominatorTree *DT) { + // Limit recursion depth to limit compile time in crazy cases. + unsigned MaxLookup = MaxLookupSearchDepth; + SearchTimes++; + + unsigned MaxPointerSize = getMaxPointerSize(DL); + Decomposed.VarIndices.clear(); + do { + // See if this is a bitcast or GEP. + const Operator *Op = dyn_cast<Operator>(V); + if (!Op) { + // The only non-operator case we can handle are GlobalAliases. + if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { + if (!GA->isInterposable()) { + V = GA->getAliasee(); + continue; + } + } + Decomposed.Base = V; + return false; + } + + if (Op->getOpcode() == Instruction::BitCast || + Op->getOpcode() == Instruction::AddrSpaceCast) { + V = Op->getOperand(0); + continue; + } + + const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op); + if (!GEPOp) { + if (const auto *Call = dyn_cast<CallBase>(V)) { + // CaptureTracking can know about special capturing properties of some + // intrinsics like launder.invariant.group, that can't be expressed with + // the attributes, but have properties like returning aliasing pointer. + // Because some analysis may assume that nocaptured pointer is not + // returned from some special intrinsic (because function would have to + // be marked with returns attribute), it is crucial to use this function + // because it should be in sync with CaptureTracking. Not using it may + // cause weird miscompilations where 2 aliasing pointers are assumed to + // noalias. + if (auto *RP = getArgumentAliasingToReturnedPointer(Call, false)) { + V = RP; + continue; + } + } + + // If it's not a GEP, hand it off to SimplifyInstruction to see if it + // can come up with something. This matches what GetUnderlyingObject does. + if (const Instruction *I = dyn_cast<Instruction>(V)) + // TODO: Get a DominatorTree and AssumptionCache and use them here + // (these are both now available in this function, but this should be + // updated when GetUnderlyingObject is updated). TLI should be + // provided also. + if (const Value *Simplified = + SimplifyInstruction(const_cast<Instruction *>(I), DL)) { + V = Simplified; + continue; + } + + Decomposed.Base = V; + return false; + } + + // Don't attempt to analyze GEPs over unsized objects. + if (!GEPOp->getSourceElementType()->isSized()) { + Decomposed.Base = V; + return false; + } + + unsigned AS = GEPOp->getPointerAddressSpace(); + // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices. + gep_type_iterator GTI = gep_type_begin(GEPOp); + unsigned PointerSize = DL.getPointerSizeInBits(AS); + // Assume all GEP operands are constants until proven otherwise. + bool GepHasConstantOffset = true; + for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end(); + I != E; ++I, ++GTI) { + const Value *Index = *I; + // Compute the (potentially symbolic) offset in bytes for this index. + if (StructType *STy = GTI.getStructTypeOrNull()) { + // For a struct, add the member offset. + unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue(); + if (FieldNo == 0) + continue; + + Decomposed.StructOffset += + DL.getStructLayout(STy)->getElementOffset(FieldNo); + continue; + } + + // For an array/pointer, add the element offset, explicitly scaled. + if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) { + if (CIdx->isZero()) + continue; + Decomposed.OtherOffset += + (DL.getTypeAllocSize(GTI.getIndexedType()) * + CIdx->getValue().sextOrSelf(MaxPointerSize)) + .sextOrTrunc(MaxPointerSize); + continue; + } + + GepHasConstantOffset = false; + + APInt Scale(MaxPointerSize, DL.getTypeAllocSize(GTI.getIndexedType())); + unsigned ZExtBits = 0, SExtBits = 0; + + // If the integer type is smaller than the pointer size, it is implicitly + // sign extended to pointer size. + unsigned Width = Index->getType()->getIntegerBitWidth(); + if (PointerSize > Width) + SExtBits += PointerSize - Width; + + // Use GetLinearExpression to decompose the index into a C1*V+C2 form. + APInt IndexScale(Width, 0), IndexOffset(Width, 0); + bool NSW = true, NUW = true; + const Value *OrigIndex = Index; + Index = GetLinearExpression(Index, IndexScale, IndexOffset, ZExtBits, + SExtBits, DL, 0, AC, DT, NSW, NUW); + + // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale. + // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale. + + // It can be the case that, even through C1*V+C2 does not overflow for + // relevant values of V, (C2*Scale) can overflow. In that case, we cannot + // decompose the expression in this way. + // + // FIXME: C1*Scale and the other operations in the decomposed + // (C1*Scale)*V+C2*Scale can also overflow. We should check for this + // possibility. + APInt WideScaledOffset = IndexOffset.sextOrTrunc(MaxPointerSize*2) * + Scale.sext(MaxPointerSize*2); + if (WideScaledOffset.getMinSignedBits() > MaxPointerSize) { + Index = OrigIndex; + IndexScale = 1; + IndexOffset = 0; + + ZExtBits = SExtBits = 0; + if (PointerSize > Width) + SExtBits += PointerSize - Width; + } else { + Decomposed.OtherOffset += IndexOffset.sextOrTrunc(MaxPointerSize) * Scale; + Scale *= IndexScale.sextOrTrunc(MaxPointerSize); + } + + // If we already had an occurrence of this index variable, merge this + // scale into it. For example, we want to handle: + // A[x][x] -> x*16 + x*4 -> x*20 + // This also ensures that 'x' only appears in the index list once. + for (unsigned i = 0, e = Decomposed.VarIndices.size(); i != e; ++i) { + if (Decomposed.VarIndices[i].V == Index && + Decomposed.VarIndices[i].ZExtBits == ZExtBits && + Decomposed.VarIndices[i].SExtBits == SExtBits) { + Scale += Decomposed.VarIndices[i].Scale; + Decomposed.VarIndices.erase(Decomposed.VarIndices.begin() + i); + break; + } + } + + // Make sure that we have a scale that makes sense for this target's + // pointer size. + Scale = adjustToPointerSize(Scale, PointerSize); + + if (!!Scale) { + VariableGEPIndex Entry = {Index, ZExtBits, SExtBits, Scale}; + Decomposed.VarIndices.push_back(Entry); + } + } + + // Take care of wrap-arounds + if (GepHasConstantOffset) { + Decomposed.StructOffset = + adjustToPointerSize(Decomposed.StructOffset, PointerSize); + Decomposed.OtherOffset = + adjustToPointerSize(Decomposed.OtherOffset, PointerSize); + } + + // Analyze the base pointer next. + V = GEPOp->getOperand(0); + } while (--MaxLookup); + + // If the chain of expressions is too deep, just return early. + Decomposed.Base = V; + SearchLimitReached++; + return true; +} + +/// Returns whether the given pointer value points to memory that is local to +/// the function, with global constants being considered local to all +/// functions. +bool BasicAAResult::pointsToConstantMemory(const MemoryLocation &Loc, + AAQueryInfo &AAQI, bool OrLocal) { + assert(Visited.empty() && "Visited must be cleared after use!"); + + unsigned MaxLookup = 8; + SmallVector<const Value *, 16> Worklist; + Worklist.push_back(Loc.Ptr); + do { + const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL); + if (!Visited.insert(V).second) { + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal); + } + + // An alloca instruction defines local memory. + if (OrLocal && isa<AllocaInst>(V)) + continue; + + // A global constant counts as local memory for our purposes. + if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) { + // Note: this doesn't require GV to be "ODR" because it isn't legal for a + // global to be marked constant in some modules and non-constant in + // others. GV may even be a declaration, not a definition. + if (!GV->isConstant()) { + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal); + } + continue; + } + + // If both select values point to local memory, then so does the select. + if (const SelectInst *SI = dyn_cast<SelectInst>(V)) { + Worklist.push_back(SI->getTrueValue()); + Worklist.push_back(SI->getFalseValue()); + continue; + } + + // If all values incoming to a phi node point to local memory, then so does + // the phi. + if (const PHINode *PN = dyn_cast<PHINode>(V)) { + // Don't bother inspecting phi nodes with many operands. + if (PN->getNumIncomingValues() > MaxLookup) { + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal); + } + for (Value *IncValue : PN->incoming_values()) + Worklist.push_back(IncValue); + continue; + } + + // Otherwise be conservative. + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal); + } while (!Worklist.empty() && --MaxLookup); + + Visited.clear(); + return Worklist.empty(); +} + +/// Returns the behavior when calling the given call site. +FunctionModRefBehavior BasicAAResult::getModRefBehavior(const CallBase *Call) { + if (Call->doesNotAccessMemory()) + // Can't do better than this. + return FMRB_DoesNotAccessMemory; + + FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior; + + // If the callsite knows it only reads memory, don't return worse + // than that. + if (Call->onlyReadsMemory()) + Min = FMRB_OnlyReadsMemory; + else if (Call->doesNotReadMemory()) + Min = FMRB_DoesNotReadMemory; + + if (Call->onlyAccessesArgMemory()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees); + else if (Call->onlyAccessesInaccessibleMemory()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem); + else if (Call->onlyAccessesInaccessibleMemOrArgMem()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem); + + // If the call has operand bundles then aliasing attributes from the function + // it calls do not directly apply to the call. This can be made more precise + // in the future. + if (!Call->hasOperandBundles()) + if (const Function *F = Call->getCalledFunction()) + Min = + FunctionModRefBehavior(Min & getBestAAResults().getModRefBehavior(F)); + + return Min; +} + +/// Returns the behavior when calling the given function. For use when the call +/// site is not known. +FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) { + // If the function declares it doesn't access memory, we can't do better. + if (F->doesNotAccessMemory()) + return FMRB_DoesNotAccessMemory; + + FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior; + + // If the function declares it only reads memory, go with that. + if (F->onlyReadsMemory()) + Min = FMRB_OnlyReadsMemory; + else if (F->doesNotReadMemory()) + Min = FMRB_DoesNotReadMemory; + + if (F->onlyAccessesArgMemory()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees); + else if (F->onlyAccessesInaccessibleMemory()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem); + else if (F->onlyAccessesInaccessibleMemOrArgMem()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem); + + return Min; +} + +/// Returns true if this is a writeonly (i.e Mod only) parameter. +static bool isWriteOnlyParam(const CallBase *Call, unsigned ArgIdx, + const TargetLibraryInfo &TLI) { + if (Call->paramHasAttr(ArgIdx, Attribute::WriteOnly)) + return true; + + // We can bound the aliasing properties of memset_pattern16 just as we can + // for memcpy/memset. This is particularly important because the + // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16 + // whenever possible. + // FIXME Consider handling this in InferFunctionAttr.cpp together with other + // attributes. + LibFunc F; + if (Call->getCalledFunction() && + TLI.getLibFunc(*Call->getCalledFunction(), F) && + F == LibFunc_memset_pattern16 && TLI.has(F)) + if (ArgIdx == 0) + return true; + + // TODO: memset_pattern4, memset_pattern8 + // TODO: _chk variants + // TODO: strcmp, strcpy + + return false; +} + +ModRefInfo BasicAAResult::getArgModRefInfo(const CallBase *Call, + unsigned ArgIdx) { + // Checking for known builtin intrinsics and target library functions. + if (isWriteOnlyParam(Call, ArgIdx, TLI)) + return ModRefInfo::Mod; + + if (Call->paramHasAttr(ArgIdx, Attribute::ReadOnly)) + return ModRefInfo::Ref; + + if (Call->paramHasAttr(ArgIdx, Attribute::ReadNone)) + return ModRefInfo::NoModRef; + + return AAResultBase::getArgModRefInfo(Call, ArgIdx); +} + +static bool isIntrinsicCall(const CallBase *Call, Intrinsic::ID IID) { + const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Call); + return II && II->getIntrinsicID() == IID; +} + +#ifndef NDEBUG +static const Function *getParent(const Value *V) { + if (const Instruction *inst = dyn_cast<Instruction>(V)) { + if (!inst->getParent()) + return nullptr; + return inst->getParent()->getParent(); + } + + if (const Argument *arg = dyn_cast<Argument>(V)) + return arg->getParent(); + + return nullptr; +} + +static bool notDifferentParent(const Value *O1, const Value *O2) { + + const Function *F1 = getParent(O1); + const Function *F2 = getParent(O2); + + return !F1 || !F2 || F1 == F2; +} +#endif + +AliasResult BasicAAResult::alias(const MemoryLocation &LocA, + const MemoryLocation &LocB, + AAQueryInfo &AAQI) { + assert(notDifferentParent(LocA.Ptr, LocB.Ptr) && + "BasicAliasAnalysis doesn't support interprocedural queries."); + + // If we have a directly cached entry for these locations, we have recursed + // through this once, so just return the cached results. Notably, when this + // happens, we don't clear the cache. + auto CacheIt = AAQI.AliasCache.find(AAQueryInfo::LocPair(LocA, LocB)); + if (CacheIt != AAQI.AliasCache.end()) + return CacheIt->second; + + CacheIt = AAQI.AliasCache.find(AAQueryInfo::LocPair(LocB, LocA)); + if (CacheIt != AAQI.AliasCache.end()) + return CacheIt->second; + + AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags, LocB.Ptr, + LocB.Size, LocB.AATags, AAQI); + + VisitedPhiBBs.clear(); + return Alias; +} + +/// Checks to see if the specified callsite can clobber the specified memory +/// object. +/// +/// Since we only look at local properties of this function, we really can't +/// say much about this query. We do, however, use simple "address taken" +/// analysis on local objects. +ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call, + const MemoryLocation &Loc, + AAQueryInfo &AAQI) { + assert(notDifferentParent(Call, Loc.Ptr) && + "AliasAnalysis query involving multiple functions!"); + + const Value *Object = GetUnderlyingObject(Loc.Ptr, DL); + + // Calls marked 'tail' cannot read or write allocas from the current frame + // because the current frame might be destroyed by the time they run. However, + // a tail call may use an alloca with byval. Calling with byval copies the + // contents of the alloca into argument registers or stack slots, so there is + // no lifetime issue. + if (isa<AllocaInst>(Object)) + if (const CallInst *CI = dyn_cast<CallInst>(Call)) + if (CI->isTailCall() && + !CI->getAttributes().hasAttrSomewhere(Attribute::ByVal)) + return ModRefInfo::NoModRef; + + // Stack restore is able to modify unescaped dynamic allocas. Assume it may + // modify them even though the alloca is not escaped. + if (auto *AI = dyn_cast<AllocaInst>(Object)) + if (!AI->isStaticAlloca() && isIntrinsicCall(Call, Intrinsic::stackrestore)) + return ModRefInfo::Mod; + + // If the pointer is to a locally allocated object that does not escape, + // then the call can not mod/ref the pointer unless the call takes the pointer + // as an argument, and itself doesn't capture it. + if (!isa<Constant>(Object) && Call != Object && + isNonEscapingLocalObject(Object, &AAQI.IsCapturedCache)) { + + // Optimistically assume that call doesn't touch Object and check this + // assumption in the following loop. + ModRefInfo Result = ModRefInfo::NoModRef; + bool IsMustAlias = true; + + unsigned OperandNo = 0; + for (auto CI = Call->data_operands_begin(), CE = Call->data_operands_end(); + CI != CE; ++CI, ++OperandNo) { + // Only look at the no-capture or byval pointer arguments. If this + // pointer were passed to arguments that were neither of these, then it + // couldn't be no-capture. + if (!(*CI)->getType()->isPointerTy() || + (!Call->doesNotCapture(OperandNo) && + OperandNo < Call->getNumArgOperands() && + !Call->isByValArgument(OperandNo))) + continue; + + // Call doesn't access memory through this operand, so we don't care + // if it aliases with Object. + if (Call->doesNotAccessMemory(OperandNo)) + continue; + + // If this is a no-capture pointer argument, see if we can tell that it + // is impossible to alias the pointer we're checking. + AliasResult AR = getBestAAResults().alias(MemoryLocation(*CI), + MemoryLocation(Object), AAQI); + if (AR != MustAlias) + IsMustAlias = false; + // Operand doesn't alias 'Object', continue looking for other aliases + if (AR == NoAlias) + continue; + // Operand aliases 'Object', but call doesn't modify it. Strengthen + // initial assumption and keep looking in case if there are more aliases. + if (Call->onlyReadsMemory(OperandNo)) { + Result = setRef(Result); + continue; + } + // Operand aliases 'Object' but call only writes into it. + if (Call->doesNotReadMemory(OperandNo)) { + Result = setMod(Result); + continue; + } + // This operand aliases 'Object' and call reads and writes into it. + // Setting ModRef will not yield an early return below, MustAlias is not + // used further. + Result = ModRefInfo::ModRef; + break; + } + + // No operand aliases, reset Must bit. Add below if at least one aliases + // and all aliases found are MustAlias. + if (isNoModRef(Result)) + IsMustAlias = false; + + // Early return if we improved mod ref information + if (!isModAndRefSet(Result)) { + if (isNoModRef(Result)) + return ModRefInfo::NoModRef; + return IsMustAlias ? setMust(Result) : clearMust(Result); + } + } + + // If the call is to malloc or calloc, we can assume that it doesn't + // modify any IR visible value. This is only valid because we assume these + // routines do not read values visible in the IR. TODO: Consider special + // casing realloc and strdup routines which access only their arguments as + // well. Or alternatively, replace all of this with inaccessiblememonly once + // that's implemented fully. + if (isMallocOrCallocLikeFn(Call, &TLI)) { + // Be conservative if the accessed pointer may alias the allocation - + // fallback to the generic handling below. + if (getBestAAResults().alias(MemoryLocation(Call), Loc, AAQI) == NoAlias) + return ModRefInfo::NoModRef; + } + + // The semantics of memcpy intrinsics forbid overlap between their respective + // operands, i.e., source and destination of any given memcpy must no-alias. + // If Loc must-aliases either one of these two locations, then it necessarily + // no-aliases the other. + if (auto *Inst = dyn_cast<AnyMemCpyInst>(Call)) { + AliasResult SrcAA, DestAA; + + if ((SrcAA = getBestAAResults().alias(MemoryLocation::getForSource(Inst), + Loc, AAQI)) == MustAlias) + // Loc is exactly the memcpy source thus disjoint from memcpy dest. + return ModRefInfo::Ref; + if ((DestAA = getBestAAResults().alias(MemoryLocation::getForDest(Inst), + Loc, AAQI)) == MustAlias) + // The converse case. + return ModRefInfo::Mod; + + // It's also possible for Loc to alias both src and dest, or neither. + ModRefInfo rv = ModRefInfo::NoModRef; + if (SrcAA != NoAlias) + rv = setRef(rv); + if (DestAA != NoAlias) + rv = setMod(rv); + return rv; + } + + // While the assume intrinsic is marked as arbitrarily writing so that + // proper control dependencies will be maintained, it never aliases any + // particular memory location. + if (isIntrinsicCall(Call, Intrinsic::assume)) + return ModRefInfo::NoModRef; + + // Like assumes, guard intrinsics are also marked as arbitrarily writing so + // that proper control dependencies are maintained but they never mods any + // particular memory location. + // + // *Unlike* assumes, guard intrinsics are modeled as reading memory since the + // heap state at the point the guard is issued needs to be consistent in case + // the guard invokes the "deopt" continuation. + if (isIntrinsicCall(Call, Intrinsic::experimental_guard)) + return ModRefInfo::Ref; + + // Like assumes, invariant.start intrinsics were also marked as arbitrarily + // writing so that proper control dependencies are maintained but they never + // mod any particular memory location visible to the IR. + // *Unlike* assumes (which are now modeled as NoModRef), invariant.start + // intrinsic is now modeled as reading memory. This prevents hoisting the + // invariant.start intrinsic over stores. Consider: + // *ptr = 40; + // *ptr = 50; + // invariant_start(ptr) + // int val = *ptr; + // print(val); + // + // This cannot be transformed to: + // + // *ptr = 40; + // invariant_start(ptr) + // *ptr = 50; + // int val = *ptr; + // print(val); + // + // The transformation will cause the second store to be ignored (based on + // rules of invariant.start) and print 40, while the first program always + // prints 50. + if (isIntrinsicCall(Call, Intrinsic::invariant_start)) + return ModRefInfo::Ref; + + // The AAResultBase base class has some smarts, lets use them. + return AAResultBase::getModRefInfo(Call, Loc, AAQI); +} + +ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call1, + const CallBase *Call2, + AAQueryInfo &AAQI) { + // While the assume intrinsic is marked as arbitrarily writing so that + // proper control dependencies will be maintained, it never aliases any + // particular memory location. + if (isIntrinsicCall(Call1, Intrinsic::assume) || + isIntrinsicCall(Call2, Intrinsic::assume)) + return ModRefInfo::NoModRef; + + // Like assumes, guard intrinsics are also marked as arbitrarily writing so + // that proper control dependencies are maintained but they never mod any + // particular memory location. + // + // *Unlike* assumes, guard intrinsics are modeled as reading memory since the + // heap state at the point the guard is issued needs to be consistent in case + // the guard invokes the "deopt" continuation. + + // NB! This function is *not* commutative, so we special case two + // possibilities for guard intrinsics. + + if (isIntrinsicCall(Call1, Intrinsic::experimental_guard)) + return isModSet(createModRefInfo(getModRefBehavior(Call2))) + ? ModRefInfo::Ref + : ModRefInfo::NoModRef; + + if (isIntrinsicCall(Call2, Intrinsic::experimental_guard)) + return isModSet(createModRefInfo(getModRefBehavior(Call1))) + ? ModRefInfo::Mod + : ModRefInfo::NoModRef; + + // The AAResultBase base class has some smarts, lets use them. + return AAResultBase::getModRefInfo(Call1, Call2, AAQI); +} + +/// Provide ad-hoc rules to disambiguate accesses through two GEP operators, +/// both having the exact same pointer operand. +static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1, + LocationSize MaybeV1Size, + const GEPOperator *GEP2, + LocationSize MaybeV2Size, + const DataLayout &DL) { + assert(GEP1->getPointerOperand()->stripPointerCastsAndInvariantGroups() == + GEP2->getPointerOperand()->stripPointerCastsAndInvariantGroups() && + GEP1->getPointerOperandType() == GEP2->getPointerOperandType() && + "Expected GEPs with the same pointer operand"); + + // Try to determine whether GEP1 and GEP2 index through arrays, into structs, + // such that the struct field accesses provably cannot alias. + // We also need at least two indices (the pointer, and the struct field). + if (GEP1->getNumIndices() != GEP2->getNumIndices() || + GEP1->getNumIndices() < 2) + return MayAlias; + + // If we don't know the size of the accesses through both GEPs, we can't + // determine whether the struct fields accessed can't alias. + if (MaybeV1Size == LocationSize::unknown() || + MaybeV2Size == LocationSize::unknown()) + return MayAlias; + + const uint64_t V1Size = MaybeV1Size.getValue(); + const uint64_t V2Size = MaybeV2Size.getValue(); + + ConstantInt *C1 = + dyn_cast<ConstantInt>(GEP1->getOperand(GEP1->getNumOperands() - 1)); + ConstantInt *C2 = + dyn_cast<ConstantInt>(GEP2->getOperand(GEP2->getNumOperands() - 1)); + + // If the last (struct) indices are constants and are equal, the other indices + // might be also be dynamically equal, so the GEPs can alias. + if (C1 && C2) { + unsigned BitWidth = std::max(C1->getBitWidth(), C2->getBitWidth()); + if (C1->getValue().sextOrSelf(BitWidth) == + C2->getValue().sextOrSelf(BitWidth)) + return MayAlias; + } + + // Find the last-indexed type of the GEP, i.e., the type you'd get if + // you stripped the last index. + // On the way, look at each indexed type. If there's something other + // than an array, different indices can lead to different final types. + SmallVector<Value *, 8> IntermediateIndices; + + // Insert the first index; we don't need to check the type indexed + // through it as it only drops the pointer indirection. + assert(GEP1->getNumIndices() > 1 && "Not enough GEP indices to examine"); + IntermediateIndices.push_back(GEP1->getOperand(1)); + + // Insert all the remaining indices but the last one. + // Also, check that they all index through arrays. + for (unsigned i = 1, e = GEP1->getNumIndices() - 1; i != e; ++i) { + if (!isa<ArrayType>(GetElementPtrInst::getIndexedType( + GEP1->getSourceElementType(), IntermediateIndices))) + return MayAlias; + IntermediateIndices.push_back(GEP1->getOperand(i + 1)); + } + + auto *Ty = GetElementPtrInst::getIndexedType( + GEP1->getSourceElementType(), IntermediateIndices); + StructType *LastIndexedStruct = dyn_cast<StructType>(Ty); + + if (isa<SequentialType>(Ty)) { + // We know that: + // - both GEPs begin indexing from the exact same pointer; + // - the last indices in both GEPs are constants, indexing into a sequential + // type (array or pointer); + // - both GEPs only index through arrays prior to that. + // + // Because array indices greater than the number of elements are valid in + // GEPs, unless we know the intermediate indices are identical between + // GEP1 and GEP2 we cannot guarantee that the last indexed arrays don't + // partially overlap. We also need to check that the loaded size matches + // the element size, otherwise we could still have overlap. + const uint64_t ElementSize = + DL.getTypeStoreSize(cast<SequentialType>(Ty)->getElementType()); + if (V1Size != ElementSize || V2Size != ElementSize) + return MayAlias; + + for (unsigned i = 0, e = GEP1->getNumIndices() - 1; i != e; ++i) + if (GEP1->getOperand(i + 1) != GEP2->getOperand(i + 1)) + return MayAlias; + + // Now we know that the array/pointer that GEP1 indexes into and that + // that GEP2 indexes into must either precisely overlap or be disjoint. + // Because they cannot partially overlap and because fields in an array + // cannot overlap, if we can prove the final indices are different between + // GEP1 and GEP2, we can conclude GEP1 and GEP2 don't alias. + + // If the last indices are constants, we've already checked they don't + // equal each other so we can exit early. + if (C1 && C2) + return NoAlias; + { + Value *GEP1LastIdx = GEP1->getOperand(GEP1->getNumOperands() - 1); + Value *GEP2LastIdx = GEP2->getOperand(GEP2->getNumOperands() - 1); + if (isa<PHINode>(GEP1LastIdx) || isa<PHINode>(GEP2LastIdx)) { + // If one of the indices is a PHI node, be safe and only use + // computeKnownBits so we don't make any assumptions about the + // relationships between the two indices. This is important if we're + // asking about values from different loop iterations. See PR32314. + // TODO: We may be able to change the check so we only do this when + // we definitely looked through a PHINode. + if (GEP1LastIdx != GEP2LastIdx && + GEP1LastIdx->getType() == GEP2LastIdx->getType()) { + KnownBits Known1 = computeKnownBits(GEP1LastIdx, DL); + KnownBits Known2 = computeKnownBits(GEP2LastIdx, DL); + if (Known1.Zero.intersects(Known2.One) || + Known1.One.intersects(Known2.Zero)) + return NoAlias; + } + } else if (isKnownNonEqual(GEP1LastIdx, GEP2LastIdx, DL)) + return NoAlias; + } + return MayAlias; + } else if (!LastIndexedStruct || !C1 || !C2) { + return MayAlias; + } + + if (C1->getValue().getActiveBits() > 64 || + C2->getValue().getActiveBits() > 64) + return MayAlias; + + // We know that: + // - both GEPs begin indexing from the exact same pointer; + // - the last indices in both GEPs are constants, indexing into a struct; + // - said indices are different, hence, the pointed-to fields are different; + // - both GEPs only index through arrays prior to that. + // + // This lets us determine that the struct that GEP1 indexes into and the + // struct that GEP2 indexes into must either precisely overlap or be + // completely disjoint. Because they cannot partially overlap, indexing into + // different non-overlapping fields of the struct will never alias. + + // Therefore, the only remaining thing needed to show that both GEPs can't + // alias is that the fields are not overlapping. + const StructLayout *SL = DL.getStructLayout(LastIndexedStruct); + const uint64_t StructSize = SL->getSizeInBytes(); + const uint64_t V1Off = SL->getElementOffset(C1->getZExtValue()); + const uint64_t V2Off = SL->getElementOffset(C2->getZExtValue()); + + auto EltsDontOverlap = [StructSize](uint64_t V1Off, uint64_t V1Size, + uint64_t V2Off, uint64_t V2Size) { + return V1Off < V2Off && V1Off + V1Size <= V2Off && + ((V2Off + V2Size <= StructSize) || + (V2Off + V2Size - StructSize <= V1Off)); + }; + + if (EltsDontOverlap(V1Off, V1Size, V2Off, V2Size) || + EltsDontOverlap(V2Off, V2Size, V1Off, V1Size)) + return NoAlias; + + return MayAlias; +} + +// If a we have (a) a GEP and (b) a pointer based on an alloca, and the +// beginning of the object the GEP points would have a negative offset with +// repsect to the alloca, that means the GEP can not alias pointer (b). +// Note that the pointer based on the alloca may not be a GEP. For +// example, it may be the alloca itself. +// The same applies if (b) is based on a GlobalVariable. Note that just being +// based on isIdentifiedObject() is not enough - we need an identified object +// that does not permit access to negative offsets. For example, a negative +// offset from a noalias argument or call can be inbounds w.r.t the actual +// underlying object. +// +// For example, consider: +// +// struct { int f0, int f1, ...} foo; +// foo alloca; +// foo* random = bar(alloca); +// int *f0 = &alloca.f0 +// int *f1 = &random->f1; +// +// Which is lowered, approximately, to: +// +// %alloca = alloca %struct.foo +// %random = call %struct.foo* @random(%struct.foo* %alloca) +// %f0 = getelementptr inbounds %struct, %struct.foo* %alloca, i32 0, i32 0 +// %f1 = getelementptr inbounds %struct, %struct.foo* %random, i32 0, i32 1 +// +// Assume %f1 and %f0 alias. Then %f1 would point into the object allocated +// by %alloca. Since the %f1 GEP is inbounds, that means %random must also +// point into the same object. But since %f0 points to the beginning of %alloca, +// the highest %f1 can be is (%alloca + 3). This means %random can not be higher +// than (%alloca - 1), and so is not inbounds, a contradiction. +bool BasicAAResult::isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp, + const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject, + LocationSize MaybeObjectAccessSize) { + // If the object access size is unknown, or the GEP isn't inbounds, bail. + if (MaybeObjectAccessSize == LocationSize::unknown() || !GEPOp->isInBounds()) + return false; + + const uint64_t ObjectAccessSize = MaybeObjectAccessSize.getValue(); + + // We need the object to be an alloca or a globalvariable, and want to know + // the offset of the pointer from the object precisely, so no variable + // indices are allowed. + if (!(isa<AllocaInst>(DecompObject.Base) || + isa<GlobalVariable>(DecompObject.Base)) || + !DecompObject.VarIndices.empty()) + return false; + + APInt ObjectBaseOffset = DecompObject.StructOffset + + DecompObject.OtherOffset; + + // If the GEP has no variable indices, we know the precise offset + // from the base, then use it. If the GEP has variable indices, + // we can't get exact GEP offset to identify pointer alias. So return + // false in that case. + if (!DecompGEP.VarIndices.empty()) + return false; + + APInt GEPBaseOffset = DecompGEP.StructOffset; + GEPBaseOffset += DecompGEP.OtherOffset; + + return GEPBaseOffset.sge(ObjectBaseOffset + (int64_t)ObjectAccessSize); +} + +/// Provides a bunch of ad-hoc rules to disambiguate a GEP instruction against +/// another pointer. +/// +/// We know that V1 is a GEP, but we don't know anything about V2. +/// UnderlyingV1 is GetUnderlyingObject(GEP1, DL), UnderlyingV2 is the same for +/// V2. +AliasResult BasicAAResult::aliasGEP( + const GEPOperator *GEP1, LocationSize V1Size, const AAMDNodes &V1AAInfo, + const Value *V2, LocationSize V2Size, const AAMDNodes &V2AAInfo, + const Value *UnderlyingV1, const Value *UnderlyingV2, AAQueryInfo &AAQI) { + DecomposedGEP DecompGEP1, DecompGEP2; + unsigned MaxPointerSize = getMaxPointerSize(DL); + DecompGEP1.StructOffset = DecompGEP1.OtherOffset = APInt(MaxPointerSize, 0); + DecompGEP2.StructOffset = DecompGEP2.OtherOffset = APInt(MaxPointerSize, 0); + + bool GEP1MaxLookupReached = + DecomposeGEPExpression(GEP1, DecompGEP1, DL, &AC, DT); + bool GEP2MaxLookupReached = + DecomposeGEPExpression(V2, DecompGEP2, DL, &AC, DT); + + APInt GEP1BaseOffset = DecompGEP1.StructOffset + DecompGEP1.OtherOffset; + APInt GEP2BaseOffset = DecompGEP2.StructOffset + DecompGEP2.OtherOffset; + + assert(DecompGEP1.Base == UnderlyingV1 && DecompGEP2.Base == UnderlyingV2 && + "DecomposeGEPExpression returned a result different from " + "GetUnderlyingObject"); + + // If the GEP's offset relative to its base is such that the base would + // fall below the start of the object underlying V2, then the GEP and V2 + // cannot alias. + if (!GEP1MaxLookupReached && !GEP2MaxLookupReached && + isGEPBaseAtNegativeOffset(GEP1, DecompGEP1, DecompGEP2, V2Size)) + return NoAlias; + // If we have two gep instructions with must-alias or not-alias'ing base + // pointers, figure out if the indexes to the GEP tell us anything about the + // derived pointer. + if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) { + // Check for the GEP base being at a negative offset, this time in the other + // direction. + if (!GEP1MaxLookupReached && !GEP2MaxLookupReached && + isGEPBaseAtNegativeOffset(GEP2, DecompGEP2, DecompGEP1, V1Size)) + return NoAlias; + // Do the base pointers alias? + AliasResult BaseAlias = + aliasCheck(UnderlyingV1, LocationSize::unknown(), AAMDNodes(), + UnderlyingV2, LocationSize::unknown(), AAMDNodes(), AAQI); + + // Check for geps of non-aliasing underlying pointers where the offsets are + // identical. + if ((BaseAlias == MayAlias) && V1Size == V2Size) { + // Do the base pointers alias assuming type and size. + AliasResult PreciseBaseAlias = aliasCheck( + UnderlyingV1, V1Size, V1AAInfo, UnderlyingV2, V2Size, V2AAInfo, AAQI); + if (PreciseBaseAlias == NoAlias) { + // See if the computed offset from the common pointer tells us about the + // relation of the resulting pointer. + // If the max search depth is reached the result is undefined + if (GEP2MaxLookupReached || GEP1MaxLookupReached) + return MayAlias; + + // Same offsets. + if (GEP1BaseOffset == GEP2BaseOffset && + DecompGEP1.VarIndices == DecompGEP2.VarIndices) + return NoAlias; + } + } + + // If we get a No or May, then return it immediately, no amount of analysis + // will improve this situation. + if (BaseAlias != MustAlias) { + assert(BaseAlias == NoAlias || BaseAlias == MayAlias); + return BaseAlias; + } + + // Otherwise, we have a MustAlias. Since the base pointers alias each other + // exactly, see if the computed offset from the common pointer tells us + // about the relation of the resulting pointer. + // If we know the two GEPs are based off of the exact same pointer (and not + // just the same underlying object), see if that tells us anything about + // the resulting pointers. + if (GEP1->getPointerOperand()->stripPointerCastsAndInvariantGroups() == + GEP2->getPointerOperand()->stripPointerCastsAndInvariantGroups() && + GEP1->getPointerOperandType() == GEP2->getPointerOperandType()) { + AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, DL); + // If we couldn't find anything interesting, don't abandon just yet. + if (R != MayAlias) + return R; + } + + // If the max search depth is reached, the result is undefined + if (GEP2MaxLookupReached || GEP1MaxLookupReached) + return MayAlias; + + // Subtract the GEP2 pointer from the GEP1 pointer to find out their + // symbolic difference. + GEP1BaseOffset -= GEP2BaseOffset; + GetIndexDifference(DecompGEP1.VarIndices, DecompGEP2.VarIndices); + + } else { + // Check to see if these two pointers are related by the getelementptr + // instruction. If one pointer is a GEP with a non-zero index of the other + // pointer, we know they cannot alias. + + // If both accesses are unknown size, we can't do anything useful here. + if (V1Size == LocationSize::unknown() && V2Size == LocationSize::unknown()) + return MayAlias; + + AliasResult R = aliasCheck(UnderlyingV1, LocationSize::unknown(), + AAMDNodes(), V2, LocationSize::unknown(), + V2AAInfo, AAQI, nullptr, UnderlyingV2); + if (R != MustAlias) { + // If V2 may alias GEP base pointer, conservatively returns MayAlias. + // If V2 is known not to alias GEP base pointer, then the two values + // cannot alias per GEP semantics: "Any memory access must be done through + // a pointer value associated with an address range of the memory access, + // otherwise the behavior is undefined.". + assert(R == NoAlias || R == MayAlias); + return R; + } + + // If the max search depth is reached the result is undefined + if (GEP1MaxLookupReached) + return MayAlias; + } + + // In the two GEP Case, if there is no difference in the offsets of the + // computed pointers, the resultant pointers are a must alias. This + // happens when we have two lexically identical GEP's (for example). + // + // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 + // must aliases the GEP, the end result is a must alias also. + if (GEP1BaseOffset == 0 && DecompGEP1.VarIndices.empty()) + return MustAlias; + + // If there is a constant difference between the pointers, but the difference + // is less than the size of the associated memory object, then we know + // that the objects are partially overlapping. If the difference is + // greater, we know they do not overlap. + if (GEP1BaseOffset != 0 && DecompGEP1.VarIndices.empty()) { + if (GEP1BaseOffset.sge(0)) { + if (V2Size != LocationSize::unknown()) { + if (GEP1BaseOffset.ult(V2Size.getValue())) + return PartialAlias; + return NoAlias; + } + } else { + // We have the situation where: + // + + + // | BaseOffset | + // ---------------->| + // |-->V1Size |-------> V2Size + // GEP1 V2 + // We need to know that V2Size is not unknown, otherwise we might have + // stripped a gep with negative index ('gep <ptr>, -1, ...). + if (V1Size != LocationSize::unknown() && + V2Size != LocationSize::unknown()) { + if ((-GEP1BaseOffset).ult(V1Size.getValue())) + return PartialAlias; + return NoAlias; + } + } + } + + if (!DecompGEP1.VarIndices.empty()) { + APInt Modulo(MaxPointerSize, 0); + bool AllPositive = true; + for (unsigned i = 0, e = DecompGEP1.VarIndices.size(); i != e; ++i) { + + // Try to distinguish something like &A[i][1] against &A[42][0]. + // Grab the least significant bit set in any of the scales. We + // don't need std::abs here (even if the scale's negative) as we'll + // be ^'ing Modulo with itself later. + Modulo |= DecompGEP1.VarIndices[i].Scale; + + if (AllPositive) { + // If the Value could change between cycles, then any reasoning about + // the Value this cycle may not hold in the next cycle. We'll just + // give up if we can't determine conditions that hold for every cycle: + const Value *V = DecompGEP1.VarIndices[i].V; + + KnownBits Known = computeKnownBits(V, DL, 0, &AC, nullptr, DT); + bool SignKnownZero = Known.isNonNegative(); + bool SignKnownOne = Known.isNegative(); + + // Zero-extension widens the variable, and so forces the sign + // bit to zero. + bool IsZExt = DecompGEP1.VarIndices[i].ZExtBits > 0 || isa<ZExtInst>(V); + SignKnownZero |= IsZExt; + SignKnownOne &= !IsZExt; + + // If the variable begins with a zero then we know it's + // positive, regardless of whether the value is signed or + // unsigned. + APInt Scale = DecompGEP1.VarIndices[i].Scale; + AllPositive = + (SignKnownZero && Scale.sge(0)) || (SignKnownOne && Scale.slt(0)); + } + } + + Modulo = Modulo ^ (Modulo & (Modulo - 1)); + + // We can compute the difference between the two addresses + // mod Modulo. Check whether that difference guarantees that the + // two locations do not alias. + APInt ModOffset = GEP1BaseOffset & (Modulo - 1); + if (V1Size != LocationSize::unknown() && + V2Size != LocationSize::unknown() && ModOffset.uge(V2Size.getValue()) && + (Modulo - ModOffset).uge(V1Size.getValue())) + return NoAlias; + + // If we know all the variables are positive, then GEP1 >= GEP1BasePtr. + // If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers + // don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr. + if (AllPositive && GEP1BaseOffset.sgt(0) && + V2Size != LocationSize::unknown() && + GEP1BaseOffset.uge(V2Size.getValue())) + return NoAlias; + + if (constantOffsetHeuristic(DecompGEP1.VarIndices, V1Size, V2Size, + GEP1BaseOffset, &AC, DT)) + return NoAlias; + } + + // Statically, we can see that the base objects are the same, but the + // pointers have dynamic offsets which we can't resolve. And none of our + // little tricks above worked. + return MayAlias; +} + +static AliasResult MergeAliasResults(AliasResult A, AliasResult B) { + // If the results agree, take it. + if (A == B) + return A; + // A mix of PartialAlias and MustAlias is PartialAlias. + if ((A == PartialAlias && B == MustAlias) || + (B == PartialAlias && A == MustAlias)) + return PartialAlias; + // Otherwise, we don't know anything. + return MayAlias; +} + +/// Provides a bunch of ad-hoc rules to disambiguate a Select instruction +/// against another. +AliasResult +BasicAAResult::aliasSelect(const SelectInst *SI, LocationSize SISize, + const AAMDNodes &SIAAInfo, const Value *V2, + LocationSize V2Size, const AAMDNodes &V2AAInfo, + const Value *UnderV2, AAQueryInfo &AAQI) { + // If the values are Selects with the same condition, we can do a more precise + // check: just check for aliases between the values on corresponding arms. + if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2)) + if (SI->getCondition() == SI2->getCondition()) { + AliasResult Alias = + aliasCheck(SI->getTrueValue(), SISize, SIAAInfo, SI2->getTrueValue(), + V2Size, V2AAInfo, AAQI); + if (Alias == MayAlias) + return MayAlias; + AliasResult ThisAlias = + aliasCheck(SI->getFalseValue(), SISize, SIAAInfo, + SI2->getFalseValue(), V2Size, V2AAInfo, AAQI); + return MergeAliasResults(ThisAlias, Alias); + } + + // If both arms of the Select node NoAlias or MustAlias V2, then returns + // NoAlias / MustAlias. Otherwise, returns MayAlias. + AliasResult Alias = aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(), + SISize, SIAAInfo, AAQI, UnderV2); + if (Alias == MayAlias) + return MayAlias; + + AliasResult ThisAlias = aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), + SISize, SIAAInfo, AAQI, UnderV2); + return MergeAliasResults(ThisAlias, Alias); +} + +/// Provide a bunch of ad-hoc rules to disambiguate a PHI instruction against +/// another. +AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize, + const AAMDNodes &PNAAInfo, const Value *V2, + LocationSize V2Size, + const AAMDNodes &V2AAInfo, + const Value *UnderV2, AAQueryInfo &AAQI) { + // Track phi nodes we have visited. We use this information when we determine + // value equivalence. + VisitedPhiBBs.insert(PN->getParent()); + + // If the values are PHIs in the same block, we can do a more precise + // as well as efficient check: just check for aliases between the values + // on corresponding edges. + if (const PHINode *PN2 = dyn_cast<PHINode>(V2)) + if (PN2->getParent() == PN->getParent()) { + AAQueryInfo::LocPair Locs(MemoryLocation(PN, PNSize, PNAAInfo), + MemoryLocation(V2, V2Size, V2AAInfo)); + if (PN > V2) + std::swap(Locs.first, Locs.second); + // Analyse the PHIs' inputs under the assumption that the PHIs are + // NoAlias. + // If the PHIs are May/MustAlias there must be (recursively) an input + // operand from outside the PHIs' cycle that is MayAlias/MustAlias or + // there must be an operation on the PHIs within the PHIs' value cycle + // that causes a MayAlias. + // Pretend the phis do not alias. + AliasResult Alias = NoAlias; + AliasResult OrigAliasResult; + { + // Limited lifetime iterator invalidated by the aliasCheck call below. + auto CacheIt = AAQI.AliasCache.find(Locs); + assert((CacheIt != AAQI.AliasCache.end()) && + "There must exist an entry for the phi node"); + OrigAliasResult = CacheIt->second; + CacheIt->second = NoAlias; + } + + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + AliasResult ThisAlias = + aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo, + PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), + V2Size, V2AAInfo, AAQI); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; + } + + // Reset if speculation failed. + if (Alias != NoAlias) { + auto Pair = + AAQI.AliasCache.insert(std::make_pair(Locs, OrigAliasResult)); + assert(!Pair.second && "Entry must have existed"); + Pair.first->second = OrigAliasResult; + } + return Alias; + } + + SmallVector<Value *, 4> V1Srcs; + bool isRecursive = false; + if (PV) { + // If we have PhiValues then use it to get the underlying phi values. + const PhiValues::ValueSet &PhiValueSet = PV->getValuesForPhi(PN); + // If we have more phi values than the search depth then return MayAlias + // conservatively to avoid compile time explosion. The worst possible case + // is if both sides are PHI nodes. In which case, this is O(m x n) time + // where 'm' and 'n' are the number of PHI sources. + if (PhiValueSet.size() > MaxLookupSearchDepth) + return MayAlias; + // Add the values to V1Srcs + for (Value *PV1 : PhiValueSet) { + if (EnableRecPhiAnalysis) { + if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) { + // Check whether the incoming value is a GEP that advances the pointer + // result of this PHI node (e.g. in a loop). If this is the case, we + // would recurse and always get a MayAlias. Handle this case specially + // below. + if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 && + isa<ConstantInt>(PV1GEP->idx_begin())) { + isRecursive = true; + continue; + } + } + } + V1Srcs.push_back(PV1); + } + } else { + // If we don't have PhiInfo then just look at the operands of the phi itself + // FIXME: Remove this once we can guarantee that we have PhiInfo always + SmallPtrSet<Value *, 4> UniqueSrc; + for (Value *PV1 : PN->incoming_values()) { + if (isa<PHINode>(PV1)) + // If any of the source itself is a PHI, return MayAlias conservatively + // to avoid compile time explosion. The worst possible case is if both + // sides are PHI nodes. In which case, this is O(m x n) time where 'm' + // and 'n' are the number of PHI sources. + return MayAlias; + + if (EnableRecPhiAnalysis) + if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) { + // Check whether the incoming value is a GEP that advances the pointer + // result of this PHI node (e.g. in a loop). If this is the case, we + // would recurse and always get a MayAlias. Handle this case specially + // below. + if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 && + isa<ConstantInt>(PV1GEP->idx_begin())) { + isRecursive = true; + continue; + } + } + + if (UniqueSrc.insert(PV1).second) + V1Srcs.push_back(PV1); + } + } + + // If V1Srcs is empty then that means that the phi has no underlying non-phi + // value. This should only be possible in blocks unreachable from the entry + // block, but return MayAlias just in case. + if (V1Srcs.empty()) + return MayAlias; + + // If this PHI node is recursive, set the size of the accessed memory to + // unknown to represent all the possible values the GEP could advance the + // pointer to. + if (isRecursive) + PNSize = LocationSize::unknown(); + + AliasResult Alias = aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0], PNSize, + PNAAInfo, AAQI, UnderV2); + + // Early exit if the check of the first PHI source against V2 is MayAlias. + // Other results are not possible. + if (Alias == MayAlias) + return MayAlias; + + // If all sources of the PHI node NoAlias or MustAlias V2, then returns + // NoAlias / MustAlias. Otherwise, returns MayAlias. + for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { + Value *V = V1Srcs[i]; + + AliasResult ThisAlias = + aliasCheck(V2, V2Size, V2AAInfo, V, PNSize, PNAAInfo, AAQI, UnderV2); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; + } + + return Alias; +} + +/// Provides a bunch of ad-hoc rules to disambiguate in common cases, such as +/// array references. +AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size, + AAMDNodes V1AAInfo, const Value *V2, + LocationSize V2Size, AAMDNodes V2AAInfo, + AAQueryInfo &AAQI, const Value *O1, + const Value *O2) { + // If either of the memory references is empty, it doesn't matter what the + // pointer values are. + if (V1Size.isZero() || V2Size.isZero()) + return NoAlias; + + // Strip off any casts if they exist. + V1 = V1->stripPointerCastsAndInvariantGroups(); + V2 = V2->stripPointerCastsAndInvariantGroups(); + + // If V1 or V2 is undef, the result is NoAlias because we can always pick a + // value for undef that aliases nothing in the program. + if (isa<UndefValue>(V1) || isa<UndefValue>(V2)) + return NoAlias; + + // Are we checking for alias of the same value? + // Because we look 'through' phi nodes, we could look at "Value" pointers from + // different iterations. We must therefore make sure that this is not the + // case. The function isValueEqualInPotentialCycles ensures that this cannot + // happen by looking at the visited phi nodes and making sure they cannot + // reach the value. + if (isValueEqualInPotentialCycles(V1, V2)) + return MustAlias; + + if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy()) + return NoAlias; // Scalars cannot alias each other + + // Figure out what objects these things are pointing to if we can. + if (O1 == nullptr) + O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth); + + if (O2 == nullptr) + O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth); + + // Null values in the default address space don't point to any object, so they + // don't alias any other pointer. + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1)) + if (!NullPointerIsDefined(&F, CPN->getType()->getAddressSpace())) + return NoAlias; + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2)) + if (!NullPointerIsDefined(&F, CPN->getType()->getAddressSpace())) + return NoAlias; + + if (O1 != O2) { + // If V1/V2 point to two different objects, we know that we have no alias. + if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) + return NoAlias; + + // Constant pointers can't alias with non-const isIdentifiedObject objects. + if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) || + (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1))) + return NoAlias; + + // Function arguments can't alias with things that are known to be + // unambigously identified at the function level. + if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) || + (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1))) + return NoAlias; + + // If one pointer is the result of a call/invoke or load and the other is a + // non-escaping local object within the same function, then we know the + // object couldn't escape to a point where the call could return it. + // + // Note that if the pointers are in different functions, there are a + // variety of complications. A call with a nocapture argument may still + // temporary store the nocapture argument's value in a temporary memory + // location if that memory location doesn't escape. Or it may pass a + // nocapture value to other functions as long as they don't capture it. + if (isEscapeSource(O1) && + isNonEscapingLocalObject(O2, &AAQI.IsCapturedCache)) + return NoAlias; + if (isEscapeSource(O2) && + isNonEscapingLocalObject(O1, &AAQI.IsCapturedCache)) + return NoAlias; + } + + // If the size of one access is larger than the entire object on the other + // side, then we know such behavior is undefined and can assume no alias. + bool NullIsValidLocation = NullPointerIsDefined(&F); + if ((isObjectSmallerThan( + O2, getMinimalExtentFrom(*V1, V1Size, DL, NullIsValidLocation), DL, + TLI, NullIsValidLocation)) || + (isObjectSmallerThan( + O1, getMinimalExtentFrom(*V2, V2Size, DL, NullIsValidLocation), DL, + TLI, NullIsValidLocation))) + return NoAlias; + + // Check the cache before climbing up use-def chains. This also terminates + // otherwise infinitely recursive queries. + AAQueryInfo::LocPair Locs(MemoryLocation(V1, V1Size, V1AAInfo), + MemoryLocation(V2, V2Size, V2AAInfo)); + if (V1 > V2) + std::swap(Locs.first, Locs.second); + std::pair<AAQueryInfo::AliasCacheT::iterator, bool> Pair = + AAQI.AliasCache.try_emplace(Locs, MayAlias); + if (!Pair.second) + return Pair.first->second; + + // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the + // GEP can't simplify, we don't even look at the PHI cases. + if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) { + std::swap(V1, V2); + std::swap(V1Size, V2Size); + std::swap(O1, O2); + std::swap(V1AAInfo, V2AAInfo); + } + if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) { + AliasResult Result = + aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2, AAQI); + if (Result != MayAlias) { + auto ItInsPair = AAQI.AliasCache.insert(std::make_pair(Locs, Result)); + assert(!ItInsPair.second && "Entry must have existed"); + ItInsPair.first->second = Result; + return Result; + } + } + + if (isa<PHINode>(V2) && !isa<PHINode>(V1)) { + std::swap(V1, V2); + std::swap(O1, O2); + std::swap(V1Size, V2Size); + std::swap(V1AAInfo, V2AAInfo); + } + if (const PHINode *PN = dyn_cast<PHINode>(V1)) { + AliasResult Result = + aliasPHI(PN, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O2, AAQI); + if (Result != MayAlias) { + Pair = AAQI.AliasCache.try_emplace(Locs, Result); + assert(!Pair.second && "Entry must have existed"); + return Pair.first->second = Result; + } + } + + if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) { + std::swap(V1, V2); + std::swap(O1, O2); + std::swap(V1Size, V2Size); + std::swap(V1AAInfo, V2AAInfo); + } + if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) { + AliasResult Result = + aliasSelect(S1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O2, AAQI); + if (Result != MayAlias) { + Pair = AAQI.AliasCache.try_emplace(Locs, Result); + assert(!Pair.second && "Entry must have existed"); + return Pair.first->second = Result; + } + } + + // If both pointers are pointing into the same object and one of them + // accesses the entire object, then the accesses must overlap in some way. + if (O1 == O2) + if (V1Size.isPrecise() && V2Size.isPrecise() && + (isObjectSize(O1, V1Size.getValue(), DL, TLI, NullIsValidLocation) || + isObjectSize(O2, V2Size.getValue(), DL, TLI, NullIsValidLocation))) { + Pair = AAQI.AliasCache.try_emplace(Locs, PartialAlias); + assert(!Pair.second && "Entry must have existed"); + return Pair.first->second = PartialAlias; + } + + // Recurse back into the best AA results we have, potentially with refined + // memory locations. We have already ensured that BasicAA has a MayAlias + // cache result for these, so any recursion back into BasicAA won't loop. + AliasResult Result = getBestAAResults().alias(Locs.first, Locs.second, AAQI); + Pair = AAQI.AliasCache.try_emplace(Locs, Result); + assert(!Pair.second && "Entry must have existed"); + return Pair.first->second = Result; +} + +/// Check whether two Values can be considered equivalent. +/// +/// In addition to pointer equivalence of \p V1 and \p V2 this checks whether +/// they can not be part of a cycle in the value graph by looking at all +/// visited phi nodes an making sure that the phis cannot reach the value. We +/// have to do this because we are looking through phi nodes (That is we say +/// noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB). +bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V, + const Value *V2) { + if (V != V2) + return false; + + const Instruction *Inst = dyn_cast<Instruction>(V); + if (!Inst) + return true; + + if (VisitedPhiBBs.empty()) + return true; + + if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck) + return false; + + // Make sure that the visited phis cannot reach the Value. This ensures that + // the Values cannot come from different iterations of a potential cycle the + // phi nodes could be involved in. + for (auto *P : VisitedPhiBBs) + if (isPotentiallyReachable(&P->front(), Inst, nullptr, DT, LI)) + return false; + + return true; +} + +/// Computes the symbolic difference between two de-composed GEPs. +/// +/// Dest and Src are the variable indices from two decomposed GetElementPtr +/// instructions GEP1 and GEP2 which have common base pointers. +void BasicAAResult::GetIndexDifference( + SmallVectorImpl<VariableGEPIndex> &Dest, + const SmallVectorImpl<VariableGEPIndex> &Src) { + if (Src.empty()) + return; + + for (unsigned i = 0, e = Src.size(); i != e; ++i) { + const Value *V = Src[i].V; + unsigned ZExtBits = Src[i].ZExtBits, SExtBits = Src[i].SExtBits; + APInt Scale = Src[i].Scale; + + // Find V in Dest. This is N^2, but pointer indices almost never have more + // than a few variable indexes. + for (unsigned j = 0, e = Dest.size(); j != e; ++j) { + if (!isValueEqualInPotentialCycles(Dest[j].V, V) || + Dest[j].ZExtBits != ZExtBits || Dest[j].SExtBits != SExtBits) + continue; + + // If we found it, subtract off Scale V's from the entry in Dest. If it + // goes to zero, remove the entry. + if (Dest[j].Scale != Scale) + Dest[j].Scale -= Scale; + else + Dest.erase(Dest.begin() + j); + Scale = 0; + break; + } + + // If we didn't consume this entry, add it to the end of the Dest list. + if (!!Scale) { + VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale}; + Dest.push_back(Entry); + } + } +} + +bool BasicAAResult::constantOffsetHeuristic( + const SmallVectorImpl<VariableGEPIndex> &VarIndices, + LocationSize MaybeV1Size, LocationSize MaybeV2Size, APInt BaseOffset, + AssumptionCache *AC, DominatorTree *DT) { + if (VarIndices.size() != 2 || MaybeV1Size == LocationSize::unknown() || + MaybeV2Size == LocationSize::unknown()) + return false; + + const uint64_t V1Size = MaybeV1Size.getValue(); + const uint64_t V2Size = MaybeV2Size.getValue(); + + const VariableGEPIndex &Var0 = VarIndices[0], &Var1 = VarIndices[1]; + + if (Var0.ZExtBits != Var1.ZExtBits || Var0.SExtBits != Var1.SExtBits || + Var0.Scale != -Var1.Scale) + return false; + + unsigned Width = Var1.V->getType()->getIntegerBitWidth(); + + // We'll strip off the Extensions of Var0 and Var1 and do another round + // of GetLinearExpression decomposition. In the example above, if Var0 + // is zext(%x + 1) we should get V1 == %x and V1Offset == 1. + + APInt V0Scale(Width, 0), V0Offset(Width, 0), V1Scale(Width, 0), + V1Offset(Width, 0); + bool NSW = true, NUW = true; + unsigned V0ZExtBits = 0, V0SExtBits = 0, V1ZExtBits = 0, V1SExtBits = 0; + const Value *V0 = GetLinearExpression(Var0.V, V0Scale, V0Offset, V0ZExtBits, + V0SExtBits, DL, 0, AC, DT, NSW, NUW); + NSW = true; + NUW = true; + const Value *V1 = GetLinearExpression(Var1.V, V1Scale, V1Offset, V1ZExtBits, + V1SExtBits, DL, 0, AC, DT, NSW, NUW); + + if (V0Scale != V1Scale || V0ZExtBits != V1ZExtBits || + V0SExtBits != V1SExtBits || !isValueEqualInPotentialCycles(V0, V1)) + return false; + + // We have a hit - Var0 and Var1 only differ by a constant offset! + + // If we've been sext'ed then zext'd the maximum difference between Var0 and + // Var1 is possible to calculate, but we're just interested in the absolute + // minimum difference between the two. The minimum distance may occur due to + // wrapping; consider "add i3 %i, 5": if %i == 7 then 7 + 5 mod 8 == 4, and so + // the minimum distance between %i and %i + 5 is 3. + APInt MinDiff = V0Offset - V1Offset, Wrapped = -MinDiff; + MinDiff = APIntOps::umin(MinDiff, Wrapped); + APInt MinDiffBytes = + MinDiff.zextOrTrunc(Var0.Scale.getBitWidth()) * Var0.Scale.abs(); + + // We can't definitely say whether GEP1 is before or after V2 due to wrapping + // arithmetic (i.e. for some values of GEP1 and V2 GEP1 < V2, and for other + // values GEP1 > V2). We'll therefore only declare NoAlias if both V1Size and + // V2Size can fit in the MinDiffBytes gap. + return MinDiffBytes.uge(V1Size + BaseOffset.abs()) && + MinDiffBytes.uge(V2Size + BaseOffset.abs()); +} + +//===----------------------------------------------------------------------===// +// BasicAliasAnalysis Pass +//===----------------------------------------------------------------------===// + +AnalysisKey BasicAA::Key; + +BasicAAResult BasicAA::run(Function &F, FunctionAnalysisManager &AM) { + return BasicAAResult(F.getParent()->getDataLayout(), + F, + AM.getResult<TargetLibraryAnalysis>(F), + AM.getResult<AssumptionAnalysis>(F), + &AM.getResult<DominatorTreeAnalysis>(F), + AM.getCachedResult<LoopAnalysis>(F), + AM.getCachedResult<PhiValuesAnalysis>(F)); +} + +BasicAAWrapperPass::BasicAAWrapperPass() : FunctionPass(ID) { + initializeBasicAAWrapperPassPass(*PassRegistry::getPassRegistry()); +} + +char BasicAAWrapperPass::ID = 0; + +void BasicAAWrapperPass::anchor() {} + +INITIALIZE_PASS_BEGIN(BasicAAWrapperPass, "basicaa", + "Basic Alias Analysis (stateless AA impl)", false, true) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_END(BasicAAWrapperPass, "basicaa", + "Basic Alias Analysis (stateless AA impl)", false, true) + +FunctionPass *llvm::createBasicAAWrapperPass() { + return new BasicAAWrapperPass(); +} + +bool BasicAAWrapperPass::runOnFunction(Function &F) { + auto &ACT = getAnalysis<AssumptionCacheTracker>(); + auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>(); + auto &DTWP = getAnalysis<DominatorTreeWrapperPass>(); + auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>(); + auto *PVWP = getAnalysisIfAvailable<PhiValuesWrapperPass>(); + + Result.reset(new BasicAAResult(F.getParent()->getDataLayout(), F, + TLIWP.getTLI(F), ACT.getAssumptionCache(F), + &DTWP.getDomTree(), + LIWP ? &LIWP->getLoopInfo() : nullptr, + PVWP ? &PVWP->getResult() : nullptr)); + + return false; +} + +void BasicAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addUsedIfAvailable<PhiValuesWrapperPass>(); +} + +BasicAAResult llvm::createLegacyPMBasicAAResult(Pass &P, Function &F) { + return BasicAAResult( + F.getParent()->getDataLayout(), F, + P.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F), + P.getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F)); +} |