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+//===- 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/ScopeExit.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/MemoryBuiltins.h"
+#include "llvm/Analysis/MemoryLocation.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Argument.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/ConstantRange.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/Operator.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InitializePasses.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 "llvm/Support/SaveAndRestore.h"
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <optional>
+#include <utility>
+
+#define DEBUG_TYPE "basicaa"
+
+using namespace llvm;
+
+/// Enable analysis of recursive PHI nodes.
+static cl::opt<bool> EnableRecPhiAnalysis("basic-aa-recphi", cl::Hidden,
+ cl::init(true));
+
+static cl::opt<bool> EnableSeparateStorageAnalysis("basic-aa-separate-storage",
+ cl::Hidden, cl::init(true));
+
+/// 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");
+
+// The max limit of the search depth in DecomposeGEPExpression() and
+// getUnderlyingObject().
+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)))
+ return true;
+
+ // Otherwise this analysis result remains valid.
+ return false;
+}
+
+//===----------------------------------------------------------------------===//
+// Useful predicates
+//===----------------------------------------------------------------------===//
+
+/// Returns the size of the object specified by V or UnknownSize if unknown.
+static std::optional<TypeSize> 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 TypeSize::getFixed(Size);
+ return std::nullopt;
+}
+
+/// Returns true if we can prove that the object specified by V is smaller than
+/// Size.
+static bool isObjectSmallerThan(const Value *V, TypeSize 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.
+ std::optional<TypeSize> ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc,
+ /*RoundToAlign*/ true);
+
+ return ObjectSize && TypeSize::isKnownLT(*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 TypeSize 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. We can ignore frees, as an
+ // access after free would be undefined behavior.
+ bool CanBeNull, CanBeFreed;
+ uint64_t DerefBytes =
+ V.getPointerDereferenceableBytes(DL, CanBeNull, CanBeFreed);
+ 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().getKnownMinValue());
+ return TypeSize::getFixed(DerefBytes);
+}
+
+/// Returns true if we can prove that the object specified by V has size Size.
+static bool isObjectSize(const Value *V, TypeSize Size, const DataLayout &DL,
+ const TargetLibraryInfo &TLI, bool NullIsValidLoc) {
+ std::optional<TypeSize> ObjectSize =
+ getObjectSize(V, DL, TLI, NullIsValidLoc);
+ return ObjectSize && *ObjectSize == Size;
+}
+
+/// Return true if both V1 and V2 are VScale
+static bool areBothVScale(const Value *V1, const Value *V2) {
+ return PatternMatch::match(V1, PatternMatch::m_VScale()) &&
+ PatternMatch::match(V2, PatternMatch::m_VScale());
+}
+
+//===----------------------------------------------------------------------===//
+// CaptureInfo implementations
+//===----------------------------------------------------------------------===//
+
+CaptureInfo::~CaptureInfo() = default;
+
+bool SimpleCaptureInfo::isNotCapturedBefore(const Value *Object,
+ const Instruction *I, bool OrAt) {
+ return isNonEscapingLocalObject(Object, &IsCapturedCache);
+}
+
+static bool isNotInCycle(const Instruction *I, const DominatorTree *DT,
+ const LoopInfo *LI) {
+ BasicBlock *BB = const_cast<BasicBlock *>(I->getParent());
+ SmallVector<BasicBlock *> Succs(successors(BB));
+ return Succs.empty() ||
+ !isPotentiallyReachableFromMany(Succs, BB, nullptr, DT, LI);
+}
+
+bool EarliestEscapeInfo::isNotCapturedBefore(const Value *Object,
+ const Instruction *I, bool OrAt) {
+ if (!isIdentifiedFunctionLocal(Object))
+ return false;
+
+ auto Iter = EarliestEscapes.insert({Object, nullptr});
+ if (Iter.second) {
+ Instruction *EarliestCapture = FindEarliestCapture(
+ Object, *const_cast<Function *>(DT.getRoot()->getParent()),
+ /*ReturnCaptures=*/false, /*StoreCaptures=*/true, DT);
+ if (EarliestCapture) {
+ auto Ins = Inst2Obj.insert({EarliestCapture, {}});
+ Ins.first->second.push_back(Object);
+ }
+ Iter.first->second = EarliestCapture;
+ }
+
+ // No capturing instruction.
+ if (!Iter.first->second)
+ return true;
+
+ // No context instruction means any use is capturing.
+ if (!I)
+ return false;
+
+ if (I == Iter.first->second) {
+ if (OrAt)
+ return false;
+ return isNotInCycle(I, &DT, LI);
+ }
+
+ return !isPotentiallyReachable(Iter.first->second, I, nullptr, &DT, LI);
+}
+
+void EarliestEscapeInfo::removeInstruction(Instruction *I) {
+ auto Iter = Inst2Obj.find(I);
+ if (Iter != Inst2Obj.end()) {
+ for (const Value *Obj : Iter->second)
+ EarliestEscapes.erase(Obj);
+ Inst2Obj.erase(I);
+ }
+}
+
+//===----------------------------------------------------------------------===//
+// GetElementPtr Instruction Decomposition and Analysis
+//===----------------------------------------------------------------------===//
+
+namespace {
+/// Represents zext(sext(trunc(V))).
+struct CastedValue {
+ const Value *V;
+ unsigned ZExtBits = 0;
+ unsigned SExtBits = 0;
+ unsigned TruncBits = 0;
+ /// Whether trunc(V) is non-negative.
+ bool IsNonNegative = false;
+
+ explicit CastedValue(const Value *V) : V(V) {}
+ explicit CastedValue(const Value *V, unsigned ZExtBits, unsigned SExtBits,
+ unsigned TruncBits, bool IsNonNegative)
+ : V(V), ZExtBits(ZExtBits), SExtBits(SExtBits), TruncBits(TruncBits),
+ IsNonNegative(IsNonNegative) {}
+
+ unsigned getBitWidth() const {
+ return V->getType()->getPrimitiveSizeInBits() - TruncBits + ZExtBits +
+ SExtBits;
+ }
+
+ CastedValue withValue(const Value *NewV, bool PreserveNonNeg) const {
+ return CastedValue(NewV, ZExtBits, SExtBits, TruncBits,
+ IsNonNegative && PreserveNonNeg);
+ }
+
+ /// Replace V with zext(NewV)
+ CastedValue withZExtOfValue(const Value *NewV, bool ZExtNonNegative) const {
+ unsigned ExtendBy = V->getType()->getPrimitiveSizeInBits() -
+ NewV->getType()->getPrimitiveSizeInBits();
+ if (ExtendBy <= TruncBits)
+ // zext<nneg>(trunc(zext(NewV))) == zext<nneg>(trunc(NewV))
+ // The nneg can be preserved on the outer zext here.
+ return CastedValue(NewV, ZExtBits, SExtBits, TruncBits - ExtendBy,
+ IsNonNegative);
+
+ // zext(sext(zext(NewV))) == zext(zext(zext(NewV)))
+ ExtendBy -= TruncBits;
+ // zext<nneg>(zext(NewV)) == zext(NewV)
+ // zext(zext<nneg>(NewV)) == zext<nneg>(NewV)
+ // The nneg can be preserved from the inner zext here but must be dropped
+ // from the outer.
+ return CastedValue(NewV, ZExtBits + SExtBits + ExtendBy, 0, 0,
+ ZExtNonNegative);
+ }
+
+ /// Replace V with sext(NewV)
+ CastedValue withSExtOfValue(const Value *NewV) const {
+ unsigned ExtendBy = V->getType()->getPrimitiveSizeInBits() -
+ NewV->getType()->getPrimitiveSizeInBits();
+ if (ExtendBy <= TruncBits)
+ // zext<nneg>(trunc(sext(NewV))) == zext<nneg>(trunc(NewV))
+ // The nneg can be preserved on the outer zext here
+ return CastedValue(NewV, ZExtBits, SExtBits, TruncBits - ExtendBy,
+ IsNonNegative);
+
+ // zext(sext(sext(NewV)))
+ ExtendBy -= TruncBits;
+ // zext<nneg>(sext(sext(NewV))) = zext<nneg>(sext(NewV))
+ // The nneg can be preserved on the outer zext here
+ return CastedValue(NewV, ZExtBits, SExtBits + ExtendBy, 0, IsNonNegative);
+ }
+
+ APInt evaluateWith(APInt N) const {
+ assert(N.getBitWidth() == V->getType()->getPrimitiveSizeInBits() &&
+ "Incompatible bit width");
+ if (TruncBits) N = N.trunc(N.getBitWidth() - TruncBits);
+ if (SExtBits) N = N.sext(N.getBitWidth() + SExtBits);
+ if (ZExtBits) N = N.zext(N.getBitWidth() + ZExtBits);
+ return N;
+ }
+
+ ConstantRange evaluateWith(ConstantRange N) const {
+ assert(N.getBitWidth() == V->getType()->getPrimitiveSizeInBits() &&
+ "Incompatible bit width");
+ if (TruncBits) N = N.truncate(N.getBitWidth() - TruncBits);
+ if (SExtBits) N = N.signExtend(N.getBitWidth() + SExtBits);
+ if (ZExtBits) N = N.zeroExtend(N.getBitWidth() + ZExtBits);
+ return N;
+ }
+
+ bool canDistributeOver(bool NUW, bool NSW) const {
+ // zext(x op<nuw> y) == zext(x) op<nuw> zext(y)
+ // sext(x op<nsw> y) == sext(x) op<nsw> sext(y)
+ // trunc(x op y) == trunc(x) op trunc(y)
+ return (!ZExtBits || NUW) && (!SExtBits || NSW);
+ }
+
+ bool hasSameCastsAs(const CastedValue &Other) const {
+ if (ZExtBits == Other.ZExtBits && SExtBits == Other.SExtBits &&
+ TruncBits == Other.TruncBits)
+ return true;
+ // If either CastedValue has a nneg zext then the sext/zext bits are
+ // interchangable for that value.
+ if (IsNonNegative || Other.IsNonNegative)
+ return (ZExtBits + SExtBits == Other.ZExtBits + Other.SExtBits &&
+ TruncBits == Other.TruncBits);
+ return false;
+ }
+};
+
+/// Represents zext(sext(trunc(V))) * Scale + Offset.
+struct LinearExpression {
+ CastedValue Val;
+ APInt Scale;
+ APInt Offset;
+
+ /// True if all operations in this expression are NSW.
+ bool IsNSW;
+
+ LinearExpression(const CastedValue &Val, const APInt &Scale,
+ const APInt &Offset, bool IsNSW)
+ : Val(Val), Scale(Scale), Offset(Offset), IsNSW(IsNSW) {}
+
+ LinearExpression(const CastedValue &Val) : Val(Val), IsNSW(true) {
+ unsigned BitWidth = Val.getBitWidth();
+ Scale = APInt(BitWidth, 1);
+ Offset = APInt(BitWidth, 0);
+ }
+
+ LinearExpression mul(const APInt &Other, bool MulIsNSW) const {
+ // The check for zero offset is necessary, because generally
+ // (X +nsw Y) *nsw Z does not imply (X *nsw Z) +nsw (Y *nsw Z).
+ bool NSW = IsNSW && (Other.isOne() || (MulIsNSW && Offset.isZero()));
+ return LinearExpression(Val, Scale * Other, Offset * Other, NSW);
+ }
+};
+}
+
+/// Analyzes the specified value as a linear expression: "A*V + B", where A and
+/// B are constant integers.
+static LinearExpression GetLinearExpression(
+ const CastedValue &Val, const DataLayout &DL, unsigned Depth,
+ AssumptionCache *AC, DominatorTree *DT) {
+ // Limit our recursion depth.
+ if (Depth == 6)
+ return Val;
+
+ if (const ConstantInt *Const = dyn_cast<ConstantInt>(Val.V))
+ return LinearExpression(Val, APInt(Val.getBitWidth(), 0),
+ Val.evaluateWith(Const->getValue()), true);
+
+ if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(Val.V)) {
+ if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
+ APInt RHS = Val.evaluateWith(RHSC->getValue());
+ // The only non-OBO case we deal with is or, and only limited to the
+ // case where it is both nuw and nsw.
+ bool NUW = true, NSW = true;
+ if (isa<OverflowingBinaryOperator>(BOp)) {
+ NUW &= BOp->hasNoUnsignedWrap();
+ NSW &= BOp->hasNoSignedWrap();
+ }
+ if (!Val.canDistributeOver(NUW, NSW))
+ return Val;
+
+ // While we can distribute over trunc, we cannot preserve nowrap flags
+ // in that case.
+ if (Val.TruncBits)
+ NUW = NSW = false;
+
+ LinearExpression E(Val);
+ switch (BOp->getOpcode()) {
+ default:
+ // We don't understand this instruction, so we can't decompose it any
+ // further.
+ return Val;
+ case Instruction::Or:
+ // X|C == X+C if it is disjoint. Otherwise we can't analyze it.
+ if (!cast<PossiblyDisjointInst>(BOp)->isDisjoint())
+ return Val;
+
+ [[fallthrough]];
+ case Instruction::Add: {
+ E = GetLinearExpression(Val.withValue(BOp->getOperand(0), false), DL,
+ Depth + 1, AC, DT);
+ E.Offset += RHS;
+ E.IsNSW &= NSW;
+ break;
+ }
+ case Instruction::Sub: {
+ E = GetLinearExpression(Val.withValue(BOp->getOperand(0), false), DL,
+ Depth + 1, AC, DT);
+ E.Offset -= RHS;
+ E.IsNSW &= NSW;
+ break;
+ }
+ case Instruction::Mul:
+ E = GetLinearExpression(Val.withValue(BOp->getOperand(0), false), DL,
+ Depth + 1, AC, DT)
+ .mul(RHS, NSW);
+ break;
+ case Instruction::Shl:
+ // 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 (RHS.getLimitedValue() > Val.getBitWidth())
+ return Val;
+
+ E = GetLinearExpression(Val.withValue(BOp->getOperand(0), NSW), DL,
+ Depth + 1, AC, DT);
+ E.Offset <<= RHS.getLimitedValue();
+ E.Scale <<= RHS.getLimitedValue();
+ E.IsNSW &= NSW;
+ break;
+ }
+ return E;
+ }
+ }
+
+ if (const auto *ZExt = dyn_cast<ZExtInst>(Val.V))
+ return GetLinearExpression(
+ Val.withZExtOfValue(ZExt->getOperand(0), ZExt->hasNonNeg()), DL,
+ Depth + 1, AC, DT);
+
+ if (isa<SExtInst>(Val.V))
+ return GetLinearExpression(
+ Val.withSExtOfValue(cast<CastInst>(Val.V)->getOperand(0)),
+ DL, Depth + 1, AC, DT);
+
+ return Val;
+}
+
+/// To ensure a pointer offset fits in an integer of size IndexSize
+/// (in bits) when that size is smaller than the maximum index 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 index size is 64b.
+static void adjustToIndexSize(APInt &Offset, unsigned IndexSize) {
+ assert(IndexSize <= Offset.getBitWidth() && "Invalid IndexSize!");
+ unsigned ShiftBits = Offset.getBitWidth() - IndexSize;
+ if (ShiftBits != 0) {
+ Offset <<= ShiftBits;
+ Offset.ashrInPlace(ShiftBits);
+ }
+}
+
+namespace {
+// A linear transformation of a Value; this class represents
+// ZExt(SExt(Trunc(V, TruncBits), SExtBits), ZExtBits) * Scale.
+struct VariableGEPIndex {
+ CastedValue Val;
+ APInt Scale;
+
+ // Context instruction to use when querying information about this index.
+ const Instruction *CxtI;
+
+ /// True if all operations in this expression are NSW.
+ bool IsNSW;
+
+ /// True if the index should be subtracted rather than added. We don't simply
+ /// negate the Scale, to avoid losing the NSW flag: X - INT_MIN*1 may be
+ /// non-wrapping, while X + INT_MIN*(-1) wraps.
+ bool IsNegated;
+
+ bool hasNegatedScaleOf(const VariableGEPIndex &Other) const {
+ if (IsNegated == Other.IsNegated)
+ return Scale == -Other.Scale;
+ return Scale == Other.Scale;
+ }
+
+ void dump() const {
+ print(dbgs());
+ dbgs() << "\n";
+ }
+ void print(raw_ostream &OS) const {
+ OS << "(V=" << Val.V->getName()
+ << ", zextbits=" << Val.ZExtBits
+ << ", sextbits=" << Val.SExtBits
+ << ", truncbits=" << Val.TruncBits
+ << ", scale=" << Scale
+ << ", nsw=" << IsNSW
+ << ", negated=" << IsNegated << ")";
+ }
+};
+}
+
+// Represents the internal structure of a GEP, decomposed into a base pointer,
+// constant offsets, and variable scaled indices.
+struct BasicAAResult::DecomposedGEP {
+ // Base pointer of the GEP
+ const Value *Base;
+ // Total constant offset from base.
+ APInt Offset;
+ // Scaled variable (non-constant) indices.
+ SmallVector<VariableGEPIndex, 4> VarIndices;
+ // Are all operations inbounds GEPs or non-indexing operations?
+ // (std::nullopt iff expression doesn't involve any geps)
+ std::optional<bool> InBounds;
+
+ void dump() const {
+ print(dbgs());
+ dbgs() << "\n";
+ }
+ void print(raw_ostream &OS) const {
+ OS << "(DecomposedGEP Base=" << Base->getName()
+ << ", Offset=" << Offset
+ << ", VarIndices=[";
+ for (size_t i = 0; i < VarIndices.size(); i++) {
+ if (i != 0)
+ OS << ", ";
+ VarIndices[i].print(OS);
+ }
+ OS << "])";
+ }
+};
+
+
+/// 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.
+BasicAAResult::DecomposedGEP
+BasicAAResult::DecomposeGEPExpression(const Value *V, const DataLayout &DL,
+ AssumptionCache *AC, DominatorTree *DT) {
+ // Limit recursion depth to limit compile time in crazy cases.
+ unsigned MaxLookup = MaxLookupSearchDepth;
+ SearchTimes++;
+ const Instruction *CxtI = dyn_cast<Instruction>(V);
+
+ unsigned MaxIndexSize = DL.getMaxIndexSizeInBits();
+ DecomposedGEP Decomposed;
+ Decomposed.Offset = APInt(MaxIndexSize, 0);
+ 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 Decomposed;
+ }
+
+ 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 *PHI = dyn_cast<PHINode>(V)) {
+ // Look through single-arg phi nodes created by LCSSA.
+ if (PHI->getNumIncomingValues() == 1) {
+ V = PHI->getIncomingValue(0);
+ continue;
+ }
+ } else 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;
+ }
+ }
+
+ Decomposed.Base = V;
+ return Decomposed;
+ }
+
+ // Track whether we've seen at least one in bounds gep, and if so, whether
+ // all geps parsed were in bounds.
+ if (Decomposed.InBounds == std::nullopt)
+ Decomposed.InBounds = GEPOp->isInBounds();
+ else if (!GEPOp->isInBounds())
+ Decomposed.InBounds = false;
+
+ assert(GEPOp->getSourceElementType()->isSized() && "GEP must be sized");
+
+ unsigned AS = GEPOp->getPointerAddressSpace();
+ // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
+ gep_type_iterator GTI = gep_type_begin(GEPOp);
+ unsigned IndexSize = DL.getIndexSizeInBits(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.Offset += 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;
+
+ // Don't attempt to analyze GEPs if the scalable index is not zero.
+ TypeSize AllocTypeSize = GTI.getSequentialElementStride(DL);
+ if (AllocTypeSize.isScalable()) {
+ Decomposed.Base = V;
+ return Decomposed;
+ }
+
+ Decomposed.Offset += AllocTypeSize.getFixedValue() *
+ CIdx->getValue().sextOrTrunc(MaxIndexSize);
+ continue;
+ }
+
+ TypeSize AllocTypeSize = GTI.getSequentialElementStride(DL);
+ if (AllocTypeSize.isScalable()) {
+ Decomposed.Base = V;
+ return Decomposed;
+ }
+
+ GepHasConstantOffset = false;
+
+ // If the integer type is smaller than the index size, it is implicitly
+ // sign extended or truncated to index size.
+ unsigned Width = Index->getType()->getIntegerBitWidth();
+ unsigned SExtBits = IndexSize > Width ? IndexSize - Width : 0;
+ unsigned TruncBits = IndexSize < Width ? Width - IndexSize : 0;
+ LinearExpression LE = GetLinearExpression(
+ CastedValue(Index, 0, SExtBits, TruncBits, false), DL, 0, AC, DT);
+
+ // Scale by the type size.
+ unsigned TypeSize = AllocTypeSize.getFixedValue();
+ LE = LE.mul(APInt(IndexSize, TypeSize), GEPOp->isInBounds());
+ Decomposed.Offset += LE.Offset.sext(MaxIndexSize);
+ APInt Scale = LE.Scale.sext(MaxIndexSize);
+
+ // 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].Val.V == LE.Val.V ||
+ areBothVScale(Decomposed.VarIndices[i].Val.V, LE.Val.V)) &&
+ Decomposed.VarIndices[i].Val.hasSameCastsAs(LE.Val)) {
+ Scale += Decomposed.VarIndices[i].Scale;
+ LE.IsNSW = false; // We cannot guarantee nsw for the merge.
+ Decomposed.VarIndices.erase(Decomposed.VarIndices.begin() + i);
+ break;
+ }
+ }
+
+ // Make sure that we have a scale that makes sense for this target's
+ // index size.
+ adjustToIndexSize(Scale, IndexSize);
+
+ if (!!Scale) {
+ VariableGEPIndex Entry = {LE.Val, Scale, CxtI, LE.IsNSW,
+ /* IsNegated */ false};
+ Decomposed.VarIndices.push_back(Entry);
+ }
+ }
+
+ // Take care of wrap-arounds
+ if (GepHasConstantOffset)
+ adjustToIndexSize(Decomposed.Offset, IndexSize);
+
+ // 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 Decomposed;
+}
+
+ModRefInfo BasicAAResult::getModRefInfoMask(const MemoryLocation &Loc,
+ AAQueryInfo &AAQI,
+ bool IgnoreLocals) {
+ assert(Visited.empty() && "Visited must be cleared after use!");
+ auto _ = make_scope_exit([&] { Visited.clear(); });
+
+ unsigned MaxLookup = 8;
+ SmallVector<const Value *, 16> Worklist;
+ Worklist.push_back(Loc.Ptr);
+ ModRefInfo Result = ModRefInfo::NoModRef;
+
+ do {
+ const Value *V = getUnderlyingObject(Worklist.pop_back_val());
+ if (!Visited.insert(V).second)
+ continue;
+
+ // Ignore allocas if we were instructed to do so.
+ if (IgnoreLocals && isa<AllocaInst>(V))
+ continue;
+
+ // If the location points to memory that is known to be invariant for
+ // the life of the underlying SSA value, then we can exclude Mod from
+ // the set of valid memory effects.
+ //
+ // An argument that is marked readonly and noalias is known to be
+ // invariant while that function is executing.
+ if (const Argument *Arg = dyn_cast<Argument>(V)) {
+ if (Arg->hasNoAliasAttr() && Arg->onlyReadsMemory()) {
+ Result |= ModRefInfo::Ref;
+ continue;
+ }
+ }
+
+ // A global constant can't be mutated.
+ 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())
+ return ModRefInfo::ModRef;
+ 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)
+ return ModRefInfo::ModRef;
+ append_range(Worklist, PN->incoming_values());
+ continue;
+ }
+
+ // Otherwise be conservative.
+ return ModRefInfo::ModRef;
+ } while (!Worklist.empty() && --MaxLookup);
+
+ // If we hit the maximum number of instructions to examine, be conservative.
+ if (!Worklist.empty())
+ return ModRefInfo::ModRef;
+
+ return Result;
+}
+
+static bool isIntrinsicCall(const CallBase *Call, Intrinsic::ID IID) {
+ const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Call);
+ return II && II->getIntrinsicID() == IID;
+}
+
+/// Returns the behavior when calling the given call site.
+MemoryEffects BasicAAResult::getMemoryEffects(const CallBase *Call,
+ AAQueryInfo &AAQI) {
+ MemoryEffects Min = Call->getAttributes().getMemoryEffects();
+
+ if (const Function *F = dyn_cast<Function>(Call->getCalledOperand())) {
+ MemoryEffects FuncME = AAQI.AAR.getMemoryEffects(F);
+ // Operand bundles on the call may also read or write memory, in addition
+ // to the behavior of the called function.
+ if (Call->hasReadingOperandBundles())
+ FuncME |= MemoryEffects::readOnly();
+ if (Call->hasClobberingOperandBundles())
+ FuncME |= MemoryEffects::writeOnly();
+ Min &= FuncME;
+ }
+
+ return Min;
+}
+
+/// Returns the behavior when calling the given function. For use when the call
+/// site is not known.
+MemoryEffects BasicAAResult::getMemoryEffects(const Function *F) {
+ switch (F->getIntrinsicID()) {
+ case Intrinsic::experimental_guard:
+ case Intrinsic::experimental_deoptimize:
+ // These intrinsics can read arbitrary memory, and additionally modref
+ // inaccessible memory to model control dependence.
+ return MemoryEffects::readOnly() |
+ MemoryEffects::inaccessibleMemOnly(ModRefInfo::ModRef);
+ }
+
+ return F->getMemoryEffects();
+}
+
+ModRefInfo BasicAAResult::getArgModRefInfo(const CallBase *Call,
+ unsigned ArgIdx) {
+ if (Call->paramHasAttr(ArgIdx, Attribute::WriteOnly))
+ return ModRefInfo::Mod;
+
+ if (Call->paramHasAttr(ArgIdx, Attribute::ReadOnly))
+ return ModRefInfo::Ref;
+
+ if (Call->paramHasAttr(ArgIdx, Attribute::ReadNone))
+ return ModRefInfo::NoModRef;
+
+ return ModRefInfo::ModRef;
+}
+
+#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,
+ const Instruction *CtxI) {
+ assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
+ "BasicAliasAnalysis doesn't support interprocedural queries.");
+ return aliasCheck(LocA.Ptr, LocA.Size, LocB.Ptr, LocB.Size, AAQI, CtxI);
+}
+
+/// 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);
+
+ // 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;
+
+ // A call can access a locally allocated object either because it is passed as
+ // an argument to the call, or because it has escaped prior to the call.
+ //
+ // Make sure the object has not escaped here, and then check that none of the
+ // call arguments alias the object below.
+ if (!isa<Constant>(Object) && Call != Object &&
+ AAQI.CI->isNotCapturedBefore(Object, Call, /*OrAt*/ false)) {
+
+ // Optimistically assume that call doesn't touch Object and check this
+ // assumption in the following loop.
+ ModRefInfo Result = ModRefInfo::NoModRef;
+
+ unsigned OperandNo = 0;
+ for (auto CI = Call->data_operands_begin(), CE = Call->data_operands_end();
+ CI != CE; ++CI, ++OperandNo) {
+ if (!(*CI)->getType()->isPointerTy())
+ 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 =
+ AAQI.AAR.alias(MemoryLocation::getBeforeOrAfter(*CI),
+ MemoryLocation::getBeforeOrAfter(Object), AAQI);
+ // Operand doesn't alias 'Object', continue looking for other aliases
+ if (AR == AliasResult::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 |= ModRefInfo::Ref;
+ continue;
+ }
+ // Operand aliases 'Object' but call only writes into it.
+ if (Call->onlyWritesMemory(OperandNo)) {
+ Result |= ModRefInfo::Mod;
+ 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;
+ }
+
+ // Early return if we improved mod ref information
+ if (!isModAndRefSet(Result))
+ return Result;
+ }
+
+ // If the call is malloc/calloc like, 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 (AAQI.AAR.alias(MemoryLocation::getBeforeOrAfter(Call), Loc, AAQI) ==
+ AliasResult::NoAlias)
+ return ModRefInfo::NoModRef;
+ }
+
+ // 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;
+
+ // Be conservative.
+ return ModRefInfo::ModRef;
+}
+
+ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call1,
+ const CallBase *Call2,
+ AAQueryInfo &AAQI) {
+ // Guard intrinsics are 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.
+
+ // NB! This function is *not* commutative, so we special case two
+ // possibilities for guard intrinsics.
+
+ if (isIntrinsicCall(Call1, Intrinsic::experimental_guard))
+ return isModSet(getMemoryEffects(Call2, AAQI).getModRef())
+ ? ModRefInfo::Ref
+ : ModRefInfo::NoModRef;
+
+ if (isIntrinsicCall(Call2, Intrinsic::experimental_guard))
+ return isModSet(getMemoryEffects(Call1, AAQI).getModRef())
+ ? ModRefInfo::Mod
+ : ModRefInfo::NoModRef;
+
+ // Be conservative.
+ return ModRefInfo::ModRef;
+}
+
+/// Return true if we know V to the base address of the corresponding memory
+/// object. This implies that any address less than V must be out of bounds
+/// for the underlying object. Note that just being isIdentifiedObject() is
+/// not enough - For example, a negative offset from a noalias argument or call
+/// can be inbounds w.r.t the actual underlying object.
+static bool isBaseOfObject(const Value *V) {
+ // TODO: We can handle other cases here
+ // 1) For GC languages, arguments to functions are often required to be
+ // base pointers.
+ // 2) Result of allocation routines are often base pointers. Leverage TLI.
+ return (isa<AllocaInst>(V) || isa<GlobalVariable>(V));
+}
+
+/// 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), UnderlyingV2 is the same for
+/// V2.
+AliasResult BasicAAResult::aliasGEP(
+ const GEPOperator *GEP1, LocationSize V1Size,
+ const Value *V2, LocationSize V2Size,
+ const Value *UnderlyingV1, const Value *UnderlyingV2, AAQueryInfo &AAQI) {
+ if (!V1Size.hasValue() && !V2Size.hasValue()) {
+ // TODO: This limitation exists for compile-time reasons. Relax it if we
+ // can avoid exponential pathological cases.
+ if (!isa<GEPOperator>(V2))
+ return AliasResult::MayAlias;
+
+ // If both accesses have unknown size, we can only check whether the base
+ // objects don't alias.
+ AliasResult BaseAlias =
+ AAQI.AAR.alias(MemoryLocation::getBeforeOrAfter(UnderlyingV1),
+ MemoryLocation::getBeforeOrAfter(UnderlyingV2), AAQI);
+ return BaseAlias == AliasResult::NoAlias ? AliasResult::NoAlias
+ : AliasResult::MayAlias;
+ }
+
+ DominatorTree *DT = getDT(AAQI);
+ DecomposedGEP DecompGEP1 = DecomposeGEPExpression(GEP1, DL, &AC, DT);
+ DecomposedGEP DecompGEP2 = DecomposeGEPExpression(V2, DL, &AC, DT);
+
+ // Bail if we were not able to decompose anything.
+ if (DecompGEP1.Base == GEP1 && DecompGEP2.Base == V2)
+ return AliasResult::MayAlias;
+
+ // Subtract the GEP2 pointer from the GEP1 pointer to find out their
+ // symbolic difference.
+ subtractDecomposedGEPs(DecompGEP1, DecompGEP2, AAQI);
+
+ // If an inbounds GEP would have to start from an out of bounds address
+ // for the two to alias, then we can assume noalias.
+ // TODO: Remove !isScalable() once BasicAA fully support scalable location
+ // size
+ if (*DecompGEP1.InBounds && DecompGEP1.VarIndices.empty() &&
+ V2Size.hasValue() && !V2Size.isScalable() &&
+ DecompGEP1.Offset.sge(V2Size.getValue()) &&
+ isBaseOfObject(DecompGEP2.Base))
+ return AliasResult::NoAlias;
+
+ if (isa<GEPOperator>(V2)) {
+ // Symmetric case to above.
+ if (*DecompGEP2.InBounds && DecompGEP1.VarIndices.empty() &&
+ V1Size.hasValue() && !V1Size.isScalable() &&
+ DecompGEP1.Offset.sle(-V1Size.getValue()) &&
+ isBaseOfObject(DecompGEP1.Base))
+ return AliasResult::NoAlias;
+ }
+
+ // For GEPs with identical offsets, we can preserve the size and AAInfo
+ // when performing the alias check on the underlying objects.
+ if (DecompGEP1.Offset == 0 && DecompGEP1.VarIndices.empty())
+ return AAQI.AAR.alias(MemoryLocation(DecompGEP1.Base, V1Size),
+ MemoryLocation(DecompGEP2.Base, V2Size), AAQI);
+
+ // Do the base pointers alias?
+ AliasResult BaseAlias =
+ AAQI.AAR.alias(MemoryLocation::getBeforeOrAfter(DecompGEP1.Base),
+ MemoryLocation::getBeforeOrAfter(DecompGEP2.Base), AAQI);
+
+ // If we get a No or May, then return it immediately, no amount of analysis
+ // will improve this situation.
+ if (BaseAlias != AliasResult::MustAlias) {
+ assert(BaseAlias == AliasResult::NoAlias ||
+ BaseAlias == AliasResult::MayAlias);
+ return BaseAlias;
+ }
+
+ // 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 (DecompGEP1.VarIndices.empty()) {
+ APInt &Off = DecompGEP1.Offset;
+
+ // Initialize for Off >= 0 (V2 <= GEP1) case.
+ const Value *LeftPtr = V2;
+ const Value *RightPtr = GEP1;
+ LocationSize VLeftSize = V2Size;
+ LocationSize VRightSize = V1Size;
+ const bool Swapped = Off.isNegative();
+
+ if (Swapped) {
+ // Swap if we have the situation where:
+ // + +
+ // | BaseOffset |
+ // ---------------->|
+ // |-->V1Size |-------> V2Size
+ // GEP1 V2
+ std::swap(LeftPtr, RightPtr);
+ std::swap(VLeftSize, VRightSize);
+ Off = -Off;
+ }
+
+ if (!VLeftSize.hasValue())
+ return AliasResult::MayAlias;
+
+ const TypeSize LSize = VLeftSize.getValue();
+ if (!LSize.isScalable()) {
+ if (Off.ult(LSize)) {
+ // Conservatively drop processing if a phi was visited and/or offset is
+ // too big.
+ AliasResult AR = AliasResult::PartialAlias;
+ if (VRightSize.hasValue() && !VRightSize.isScalable() &&
+ Off.ule(INT32_MAX) && (Off + VRightSize.getValue()).ule(LSize)) {
+ // Memory referenced by right pointer is nested. Save the offset in
+ // cache. Note that originally offset estimated as GEP1-V2, but
+ // AliasResult contains the shift that represents GEP1+Offset=V2.
+ AR.setOffset(-Off.getSExtValue());
+ AR.swap(Swapped);
+ }
+ return AR;
+ }
+ return AliasResult::NoAlias;
+ } else {
+ // We can use the getVScaleRange to prove that Off >= (CR.upper * LSize).
+ ConstantRange CR = getVScaleRange(&F, Off.getBitWidth());
+ bool Overflow;
+ APInt UpperRange = CR.getUnsignedMax().umul_ov(
+ APInt(Off.getBitWidth(), LSize.getKnownMinValue()), Overflow);
+ if (!Overflow && Off.uge(UpperRange))
+ return AliasResult::NoAlias;
+ }
+ }
+
+ // VScale Alias Analysis - Given one scalable offset between accesses and a
+ // scalable typesize, we can divide each side by vscale, treating both values
+ // as a constant. We prove that Offset/vscale >= TypeSize/vscale.
+ if (DecompGEP1.VarIndices.size() == 1 &&
+ DecompGEP1.VarIndices[0].Val.TruncBits == 0 &&
+ DecompGEP1.Offset.isZero() &&
+ PatternMatch::match(DecompGEP1.VarIndices[0].Val.V,
+ PatternMatch::m_VScale())) {
+ const VariableGEPIndex &ScalableVar = DecompGEP1.VarIndices[0];
+ APInt Scale =
+ ScalableVar.IsNegated ? -ScalableVar.Scale : ScalableVar.Scale;
+ LocationSize VLeftSize = Scale.isNegative() ? V1Size : V2Size;
+
+ // Check if the offset is known to not overflow, if it does then attempt to
+ // prove it with the known values of vscale_range.
+ bool Overflows = !DecompGEP1.VarIndices[0].IsNSW;
+ if (Overflows) {
+ ConstantRange CR = getVScaleRange(&F, Scale.getBitWidth());
+ (void)CR.getSignedMax().smul_ov(Scale, Overflows);
+ }
+
+ if (!Overflows) {
+ // Note that we do not check that the typesize is scalable, as vscale >= 1
+ // so noalias still holds so long as the dependency distance is at least
+ // as big as the typesize.
+ if (VLeftSize.hasValue() &&
+ Scale.abs().uge(VLeftSize.getValue().getKnownMinValue()))
+ return AliasResult::NoAlias;
+ }
+ }
+
+ // Bail on analysing scalable LocationSize
+ if (V1Size.isScalable() || V2Size.isScalable())
+ return AliasResult::MayAlias;
+
+ // We need to know both acess sizes for all the following heuristics.
+ if (!V1Size.hasValue() || !V2Size.hasValue())
+ return AliasResult::MayAlias;
+
+ APInt GCD;
+ ConstantRange OffsetRange = ConstantRange(DecompGEP1.Offset);
+ for (unsigned i = 0, e = DecompGEP1.VarIndices.size(); i != e; ++i) {
+ const VariableGEPIndex &Index = DecompGEP1.VarIndices[i];
+ const APInt &Scale = Index.Scale;
+ APInt ScaleForGCD = Scale;
+ if (!Index.IsNSW)
+ ScaleForGCD =
+ APInt::getOneBitSet(Scale.getBitWidth(), Scale.countr_zero());
+
+ if (i == 0)
+ GCD = ScaleForGCD.abs();
+ else
+ GCD = APIntOps::GreatestCommonDivisor(GCD, ScaleForGCD.abs());
+
+ ConstantRange CR = computeConstantRange(Index.Val.V, /* ForSigned */ false,
+ true, &AC, Index.CxtI);
+ KnownBits Known =
+ computeKnownBits(Index.Val.V, DL, 0, &AC, Index.CxtI, DT);
+ CR = CR.intersectWith(
+ ConstantRange::fromKnownBits(Known, /* Signed */ true),
+ ConstantRange::Signed);
+ CR = Index.Val.evaluateWith(CR).sextOrTrunc(OffsetRange.getBitWidth());
+
+ assert(OffsetRange.getBitWidth() == Scale.getBitWidth() &&
+ "Bit widths are normalized to MaxIndexSize");
+ if (Index.IsNSW)
+ CR = CR.smul_sat(ConstantRange(Scale));
+ else
+ CR = CR.smul_fast(ConstantRange(Scale));
+
+ if (Index.IsNegated)
+ OffsetRange = OffsetRange.sub(CR);
+ else
+ OffsetRange = OffsetRange.add(CR);
+ }
+
+ // We now have accesses at two offsets from the same base:
+ // 1. (...)*GCD + DecompGEP1.Offset with size V1Size
+ // 2. 0 with size V2Size
+ // Using arithmetic modulo GCD, the accesses are at
+ // [ModOffset..ModOffset+V1Size) and [0..V2Size). If the first access fits
+ // into the range [V2Size..GCD), then we know they cannot overlap.
+ APInt ModOffset = DecompGEP1.Offset.srem(GCD);
+ if (ModOffset.isNegative())
+ ModOffset += GCD; // We want mod, not rem.
+ if (ModOffset.uge(V2Size.getValue()) &&
+ (GCD - ModOffset).uge(V1Size.getValue()))
+ return AliasResult::NoAlias;
+
+ // Compute ranges of potentially accessed bytes for both accesses. If the
+ // interseciton is empty, there can be no overlap.
+ unsigned BW = OffsetRange.getBitWidth();
+ ConstantRange Range1 = OffsetRange.add(
+ ConstantRange(APInt(BW, 0), APInt(BW, V1Size.getValue())));
+ ConstantRange Range2 =
+ ConstantRange(APInt(BW, 0), APInt(BW, V2Size.getValue()));
+ if (Range1.intersectWith(Range2).isEmptySet())
+ return AliasResult::NoAlias;
+
+ // Try to determine the range of values for VarIndex such that
+ // VarIndex <= -MinAbsVarIndex || MinAbsVarIndex <= VarIndex.
+ std::optional<APInt> MinAbsVarIndex;
+ if (DecompGEP1.VarIndices.size() == 1) {
+ // VarIndex = Scale*V.
+ const VariableGEPIndex &Var = DecompGEP1.VarIndices[0];
+ if (Var.Val.TruncBits == 0 &&
+ isKnownNonZero(Var.Val.V, SimplifyQuery(DL, DT, &AC, Var.CxtI))) {
+ // Check if abs(V*Scale) >= abs(Scale) holds in the presence of
+ // potentially wrapping math.
+ auto MultiplyByScaleNoWrap = [](const VariableGEPIndex &Var) {
+ if (Var.IsNSW)
+ return true;
+
+ int ValOrigBW = Var.Val.V->getType()->getPrimitiveSizeInBits();
+ // If Scale is small enough so that abs(V*Scale) >= abs(Scale) holds.
+ // The max value of abs(V) is 2^ValOrigBW - 1. Multiplying with a
+ // constant smaller than 2^(bitwidth(Val) - ValOrigBW) won't wrap.
+ int MaxScaleValueBW = Var.Val.getBitWidth() - ValOrigBW;
+ if (MaxScaleValueBW <= 0)
+ return false;
+ return Var.Scale.ule(
+ APInt::getMaxValue(MaxScaleValueBW).zext(Var.Scale.getBitWidth()));
+ };
+ // Refine MinAbsVarIndex, if abs(Scale*V) >= abs(Scale) holds in the
+ // presence of potentially wrapping math.
+ if (MultiplyByScaleNoWrap(Var)) {
+ // If V != 0 then abs(VarIndex) >= abs(Scale).
+ MinAbsVarIndex = Var.Scale.abs();
+ }
+ }
+ } else if (DecompGEP1.VarIndices.size() == 2) {
+ // VarIndex = Scale*V0 + (-Scale)*V1.
+ // If V0 != V1 then abs(VarIndex) >= abs(Scale).
+ // Check that MayBeCrossIteration is false, to avoid reasoning about
+ // inequality of values across loop iterations.
+ const VariableGEPIndex &Var0 = DecompGEP1.VarIndices[0];
+ const VariableGEPIndex &Var1 = DecompGEP1.VarIndices[1];
+ if (Var0.hasNegatedScaleOf(Var1) && Var0.Val.TruncBits == 0 &&
+ Var0.Val.hasSameCastsAs(Var1.Val) && !AAQI.MayBeCrossIteration &&
+ isKnownNonEqual(Var0.Val.V, Var1.Val.V, DL, &AC, /* CxtI */ nullptr,
+ DT))
+ MinAbsVarIndex = Var0.Scale.abs();
+ }
+
+ if (MinAbsVarIndex) {
+ // The constant offset will have added at least +/-MinAbsVarIndex to it.
+ APInt OffsetLo = DecompGEP1.Offset - *MinAbsVarIndex;
+ APInt OffsetHi = DecompGEP1.Offset + *MinAbsVarIndex;
+ // We know that Offset <= OffsetLo || Offset >= OffsetHi
+ if (OffsetLo.isNegative() && (-OffsetLo).uge(V1Size.getValue()) &&
+ OffsetHi.isNonNegative() && OffsetHi.uge(V2Size.getValue()))
+ return AliasResult::NoAlias;
+ }
+
+ if (constantOffsetHeuristic(DecompGEP1, V1Size, V2Size, &AC, DT, AAQI))
+ return AliasResult::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 AliasResult::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 == AliasResult::PartialAlias && B == AliasResult::MustAlias) ||
+ (B == AliasResult::PartialAlias && A == AliasResult::MustAlias))
+ return AliasResult::PartialAlias;
+ // Otherwise, we don't know anything.
+ return AliasResult::MayAlias;
+}
+
+/// Provides a bunch of ad-hoc rules to disambiguate a Select instruction
+/// against another.
+AliasResult
+BasicAAResult::aliasSelect(const SelectInst *SI, LocationSize SISize,
+ const Value *V2, LocationSize V2Size,
+ 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 (isValueEqualInPotentialCycles(SI->getCondition(), SI2->getCondition(),
+ AAQI)) {
+ AliasResult Alias =
+ AAQI.AAR.alias(MemoryLocation(SI->getTrueValue(), SISize),
+ MemoryLocation(SI2->getTrueValue(), V2Size), AAQI);
+ if (Alias == AliasResult::MayAlias)
+ return AliasResult::MayAlias;
+ AliasResult ThisAlias =
+ AAQI.AAR.alias(MemoryLocation(SI->getFalseValue(), SISize),
+ MemoryLocation(SI2->getFalseValue(), V2Size), 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 = AAQI.AAR.alias(MemoryLocation(SI->getTrueValue(), SISize),
+ MemoryLocation(V2, V2Size), AAQI);
+ if (Alias == AliasResult::MayAlias)
+ return AliasResult::MayAlias;
+
+ AliasResult ThisAlias =
+ AAQI.AAR.alias(MemoryLocation(SI->getFalseValue(), SISize),
+ MemoryLocation(V2, V2Size), AAQI);
+ 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 Value *V2, LocationSize V2Size,
+ AAQueryInfo &AAQI) {
+ if (!PN->getNumIncomingValues())
+ return AliasResult::NoAlias;
+ // 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()) {
+ std::optional<AliasResult> Alias;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ AliasResult ThisAlias = AAQI.AAR.alias(
+ MemoryLocation(PN->getIncomingValue(i), PNSize),
+ MemoryLocation(
+ PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), V2Size),
+ AAQI);
+ if (Alias)
+ *Alias = MergeAliasResults(*Alias, ThisAlias);
+ else
+ Alias = ThisAlias;
+ if (*Alias == AliasResult::MayAlias)
+ break;
+ }
+ return *Alias;
+ }
+
+ SmallVector<Value *, 4> V1Srcs;
+ // If a phi operand recurses back to the phi, we can still determine NoAlias
+ // if we don't alias the underlying objects of the other phi operands, as we
+ // know that the recursive phi needs to be based on them in some way.
+ bool isRecursive = false;
+ auto CheckForRecPhi = [&](Value *PV) {
+ if (!EnableRecPhiAnalysis)
+ return false;
+ if (getUnderlyingObject(PV) == PN) {
+ isRecursive = true;
+ return true;
+ }
+ return false;
+ };
+
+ SmallPtrSet<Value *, 4> UniqueSrc;
+ Value *OnePhi = nullptr;
+ for (Value *PV1 : PN->incoming_values()) {
+ // Skip the phi itself being the incoming value.
+ if (PV1 == PN)
+ continue;
+
+ if (isa<PHINode>(PV1)) {
+ if (OnePhi && OnePhi != PV1) {
+ // To control potential compile time explosion, we choose to be
+ // conserviate when we have more than one Phi input. It is important
+ // that we handle the single phi case as that lets us handle LCSSA
+ // phi nodes and (combined with the recursive phi handling) simple
+ // pointer induction variable patterns.
+ return AliasResult::MayAlias;
+ }
+ OnePhi = PV1;
+ }
+
+ if (CheckForRecPhi(PV1))
+ continue;
+
+ if (UniqueSrc.insert(PV1).second)
+ V1Srcs.push_back(PV1);
+ }
+
+ if (OnePhi && UniqueSrc.size() > 1)
+ // Out of an abundance of caution, allow only the trivial lcssa and
+ // recursive phi cases.
+ return AliasResult::MayAlias;
+
+ // 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 AliasResult::MayAlias;
+
+ // If this PHI node is recursive, indicate that the pointer may be moved
+ // across iterations. We can only prove NoAlias if different underlying
+ // objects are involved.
+ if (isRecursive)
+ PNSize = LocationSize::beforeOrAfterPointer();
+
+ // In the recursive alias queries below, we may compare values from two
+ // different loop iterations.
+ SaveAndRestore SavedMayBeCrossIteration(AAQI.MayBeCrossIteration, true);
+
+ AliasResult Alias = AAQI.AAR.alias(MemoryLocation(V1Srcs[0], PNSize),
+ MemoryLocation(V2, V2Size), AAQI);
+
+ // Early exit if the check of the first PHI source against V2 is MayAlias.
+ // Other results are not possible.
+ if (Alias == AliasResult::MayAlias)
+ return AliasResult::MayAlias;
+ // With recursive phis we cannot guarantee that MustAlias/PartialAlias will
+ // remain valid to all elements and needs to conservatively return MayAlias.
+ if (isRecursive && Alias != AliasResult::NoAlias)
+ return AliasResult::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 = AAQI.AAR.alias(
+ MemoryLocation(V, PNSize), MemoryLocation(V2, V2Size), AAQI);
+ Alias = MergeAliasResults(ThisAlias, Alias);
+ if (Alias == AliasResult::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,
+ const Value *V2, LocationSize V2Size,
+ AAQueryInfo &AAQI,
+ const Instruction *CtxI) {
+ // If either of the memory references is empty, it doesn't matter what the
+ // pointer values are.
+ if (V1Size.isZero() || V2Size.isZero())
+ return AliasResult::NoAlias;
+
+ // Strip off any casts if they exist.
+ V1 = V1->stripPointerCastsForAliasAnalysis();
+ V2 = V2->stripPointerCastsForAliasAnalysis();
+
+ // 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 AliasResult::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, AAQI))
+ return AliasResult::MustAlias;
+
+ if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
+ return AliasResult::NoAlias; // Scalars cannot alias each other
+
+ // Figure out what objects these things are pointing to if we can.
+ const Value *O1 = getUnderlyingObject(V1, MaxLookupSearchDepth);
+ const Value *O2 = getUnderlyingObject(V2, 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 AliasResult::NoAlias;
+ if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
+ if (!NullPointerIsDefined(&F, CPN->getType()->getAddressSpace()))
+ return AliasResult::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 AliasResult::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 AliasResult::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) && AAQI.CI->isNotCapturedBefore(
+ O2, dyn_cast<Instruction>(O1), /*OrAt*/ true))
+ return AliasResult::NoAlias;
+ if (isEscapeSource(O2) && AAQI.CI->isNotCapturedBefore(
+ O1, dyn_cast<Instruction>(O2), /*OrAt*/ true))
+ return AliasResult::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 AliasResult::NoAlias;
+
+ if (EnableSeparateStorageAnalysis) {
+ for (AssumptionCache::ResultElem &Elem : AC.assumptionsFor(O1)) {
+ if (!Elem || Elem.Index == AssumptionCache::ExprResultIdx)
+ continue;
+
+ AssumeInst *Assume = cast<AssumeInst>(Elem);
+ OperandBundleUse OBU = Assume->getOperandBundleAt(Elem.Index);
+ if (OBU.getTagName() == "separate_storage") {
+ assert(OBU.Inputs.size() == 2);
+ const Value *Hint1 = OBU.Inputs[0].get();
+ const Value *Hint2 = OBU.Inputs[1].get();
+ // This is often a no-op; instcombine rewrites this for us. No-op
+ // getUnderlyingObject calls are fast, though.
+ const Value *HintO1 = getUnderlyingObject(Hint1);
+ const Value *HintO2 = getUnderlyingObject(Hint2);
+
+ DominatorTree *DT = getDT(AAQI);
+ auto ValidAssumeForPtrContext = [&](const Value *Ptr) {
+ if (const Instruction *PtrI = dyn_cast<Instruction>(Ptr)) {
+ return isValidAssumeForContext(Assume, PtrI, DT,
+ /* AllowEphemerals */ true);
+ }
+ if (const Argument *PtrA = dyn_cast<Argument>(Ptr)) {
+ const Instruction *FirstI =
+ &*PtrA->getParent()->getEntryBlock().begin();
+ return isValidAssumeForContext(Assume, FirstI, DT,
+ /* AllowEphemerals */ true);
+ }
+ return false;
+ };
+
+ if ((O1 == HintO1 && O2 == HintO2) || (O1 == HintO2 && O2 == HintO1)) {
+ // Note that we go back to V1 and V2 for the
+ // ValidAssumeForPtrContext checks; they're dominated by O1 and O2,
+ // so strictly more assumptions are valid for them.
+ if ((CtxI && isValidAssumeForContext(Assume, CtxI, DT,
+ /* AllowEphemerals */ true)) ||
+ ValidAssumeForPtrContext(V1) || ValidAssumeForPtrContext(V2)) {
+ return AliasResult::NoAlias;
+ }
+ }
+ }
+ }
+ }
+
+ // If one the accesses may be before the accessed pointer, canonicalize this
+ // by using unknown after-pointer sizes for both accesses. This is
+ // equivalent, because regardless of which pointer is lower, one of them
+ // will always came after the other, as long as the underlying objects aren't
+ // disjoint. We do this so that the rest of BasicAA does not have to deal
+ // with accesses before the base pointer, and to improve cache utilization by
+ // merging equivalent states.
+ if (V1Size.mayBeBeforePointer() || V2Size.mayBeBeforePointer()) {
+ V1Size = LocationSize::afterPointer();
+ V2Size = LocationSize::afterPointer();
+ }
+
+ // FIXME: If this depth limit is hit, then we may cache sub-optimal results
+ // for recursive queries. For this reason, this limit is chosen to be large
+ // enough to be very rarely hit, while still being small enough to avoid
+ // stack overflows.
+ if (AAQI.Depth >= 512)
+ return AliasResult::MayAlias;
+
+ // Check the cache before climbing up use-def chains. This also terminates
+ // otherwise infinitely recursive queries. Include MayBeCrossIteration in the
+ // cache key, because some cases where MayBeCrossIteration==false returns
+ // MustAlias or NoAlias may become MayAlias under MayBeCrossIteration==true.
+ AAQueryInfo::LocPair Locs({V1, V1Size, AAQI.MayBeCrossIteration},
+ {V2, V2Size, AAQI.MayBeCrossIteration});
+ const bool Swapped = V1 > V2;
+ if (Swapped)
+ std::swap(Locs.first, Locs.second);
+ const auto &Pair = AAQI.AliasCache.try_emplace(
+ Locs, AAQueryInfo::CacheEntry{AliasResult::NoAlias, 0});
+ if (!Pair.second) {
+ auto &Entry = Pair.first->second;
+ if (!Entry.isDefinitive()) {
+ // Remember that we used an assumption. This may either be a direct use
+ // of an assumption, or a use of an entry that may itself be based on an
+ // assumption.
+ ++AAQI.NumAssumptionUses;
+ if (Entry.isAssumption())
+ ++Entry.NumAssumptionUses;
+ }
+ // Cache contains sorted {V1,V2} pairs but we should return original order.
+ auto Result = Entry.Result;
+ Result.swap(Swapped);
+ return Result;
+ }
+
+ int OrigNumAssumptionUses = AAQI.NumAssumptionUses;
+ unsigned OrigNumAssumptionBasedResults = AAQI.AssumptionBasedResults.size();
+ AliasResult Result =
+ aliasCheckRecursive(V1, V1Size, V2, V2Size, AAQI, O1, O2);
+
+ auto It = AAQI.AliasCache.find(Locs);
+ assert(It != AAQI.AliasCache.end() && "Must be in cache");
+ auto &Entry = It->second;
+
+ // Check whether a NoAlias assumption has been used, but disproven.
+ bool AssumptionDisproven =
+ Entry.NumAssumptionUses > 0 && Result != AliasResult::NoAlias;
+ if (AssumptionDisproven)
+ Result = AliasResult::MayAlias;
+
+ // This is a definitive result now, when considered as a root query.
+ AAQI.NumAssumptionUses -= Entry.NumAssumptionUses;
+ Entry.Result = Result;
+ // Cache contains sorted {V1,V2} pairs.
+ Entry.Result.swap(Swapped);
+
+ // If the assumption has been disproven, remove any results that may have
+ // been based on this assumption. Do this after the Entry updates above to
+ // avoid iterator invalidation.
+ if (AssumptionDisproven)
+ while (AAQI.AssumptionBasedResults.size() > OrigNumAssumptionBasedResults)
+ AAQI.AliasCache.erase(AAQI.AssumptionBasedResults.pop_back_val());
+
+ // The result may still be based on assumptions higher up in the chain.
+ // Remember it, so it can be purged from the cache later.
+ if (OrigNumAssumptionUses != AAQI.NumAssumptionUses &&
+ Result != AliasResult::MayAlias) {
+ AAQI.AssumptionBasedResults.push_back(Locs);
+ Entry.NumAssumptionUses = AAQueryInfo::CacheEntry::AssumptionBased;
+ } else {
+ Entry.NumAssumptionUses = AAQueryInfo::CacheEntry::Definitive;
+ }
+
+ // Depth is incremented before this function is called, so Depth==1 indicates
+ // a root query.
+ if (AAQI.Depth == 1) {
+ // Any remaining assumption based results must be based on proven
+ // assumptions, so convert them to definitive results.
+ for (const auto &Loc : AAQI.AssumptionBasedResults) {
+ auto It = AAQI.AliasCache.find(Loc);
+ if (It != AAQI.AliasCache.end())
+ It->second.NumAssumptionUses = AAQueryInfo::CacheEntry::Definitive;
+ }
+ AAQI.AssumptionBasedResults.clear();
+ AAQI.NumAssumptionUses = 0;
+ }
+ return Result;
+}
+
+AliasResult BasicAAResult::aliasCheckRecursive(
+ const Value *V1, LocationSize V1Size,
+ const Value *V2, LocationSize V2Size,
+ AAQueryInfo &AAQI, const Value *O1, const Value *O2) {
+ if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
+ AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, O1, O2, AAQI);
+ if (Result != AliasResult::MayAlias)
+ return Result;
+ } else if (const GEPOperator *GV2 = dyn_cast<GEPOperator>(V2)) {
+ AliasResult Result = aliasGEP(GV2, V2Size, V1, V1Size, O2, O1, AAQI);
+ Result.swap();
+ if (Result != AliasResult::MayAlias)
+ return Result;
+ }
+
+ if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
+ AliasResult Result = aliasPHI(PN, V1Size, V2, V2Size, AAQI);
+ if (Result != AliasResult::MayAlias)
+ return Result;
+ } else if (const PHINode *PN = dyn_cast<PHINode>(V2)) {
+ AliasResult Result = aliasPHI(PN, V2Size, V1, V1Size, AAQI);
+ Result.swap();
+ if (Result != AliasResult::MayAlias)
+ return Result;
+ }
+
+ if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
+ AliasResult Result = aliasSelect(S1, V1Size, V2, V2Size, AAQI);
+ if (Result != AliasResult::MayAlias)
+ return Result;
+ } else if (const SelectInst *S2 = dyn_cast<SelectInst>(V2)) {
+ AliasResult Result = aliasSelect(S2, V2Size, V1, V1Size, AAQI);
+ Result.swap();
+ if (Result != AliasResult::MayAlias)
+ return 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) {
+ bool NullIsValidLocation = NullPointerIsDefined(&F);
+ if (V1Size.isPrecise() && V2Size.isPrecise() &&
+ (isObjectSize(O1, V1Size.getValue(), DL, TLI, NullIsValidLocation) ||
+ isObjectSize(O2, V2Size.getValue(), DL, TLI, NullIsValidLocation)))
+ return AliasResult::PartialAlias;
+ }
+
+ return AliasResult::MayAlias;
+}
+
+/// Check whether two Values can be considered equivalent.
+///
+/// If the values may come from different cycle iterations, this will also
+/// check that the values are not part of cycle. 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,
+ const AAQueryInfo &AAQI) {
+ if (V != V2)
+ return false;
+
+ if (!AAQI.MayBeCrossIteration)
+ return true;
+
+ // Non-instructions and instructions in the entry block cannot be part of
+ // a loop.
+ const Instruction *Inst = dyn_cast<Instruction>(V);
+ if (!Inst || Inst->getParent()->isEntryBlock())
+ return true;
+
+ return isNotInCycle(Inst, getDT(AAQI), /*LI*/ nullptr);
+}
+
+/// Computes the symbolic difference between two de-composed GEPs.
+void BasicAAResult::subtractDecomposedGEPs(DecomposedGEP &DestGEP,
+ const DecomposedGEP &SrcGEP,
+ const AAQueryInfo &AAQI) {
+ DestGEP.Offset -= SrcGEP.Offset;
+ for (const VariableGEPIndex &Src : SrcGEP.VarIndices) {
+ // Find V in Dest. This is N^2, but pointer indices almost never have more
+ // than a few variable indexes.
+ bool Found = false;
+ for (auto I : enumerate(DestGEP.VarIndices)) {
+ VariableGEPIndex &Dest = I.value();
+ if ((!isValueEqualInPotentialCycles(Dest.Val.V, Src.Val.V, AAQI) &&
+ !areBothVScale(Dest.Val.V, Src.Val.V)) ||
+ !Dest.Val.hasSameCastsAs(Src.Val))
+ continue;
+
+ // Normalize IsNegated if we're going to lose the NSW flag anyway.
+ if (Dest.IsNegated) {
+ Dest.Scale = -Dest.Scale;
+ Dest.IsNegated = false;
+ Dest.IsNSW = false;
+ }
+
+ // If we found it, subtract off Scale V's from the entry in Dest. If it
+ // goes to zero, remove the entry.
+ if (Dest.Scale != Src.Scale) {
+ Dest.Scale -= Src.Scale;
+ Dest.IsNSW = false;
+ } else {
+ DestGEP.VarIndices.erase(DestGEP.VarIndices.begin() + I.index());
+ }
+ Found = true;
+ break;
+ }
+
+ // If we didn't consume this entry, add it to the end of the Dest list.
+ if (!Found) {
+ VariableGEPIndex Entry = {Src.Val, Src.Scale, Src.CxtI, Src.IsNSW,
+ /* IsNegated */ true};
+ DestGEP.VarIndices.push_back(Entry);
+ }
+ }
+}
+
+bool BasicAAResult::constantOffsetHeuristic(const DecomposedGEP &GEP,
+ LocationSize MaybeV1Size,
+ LocationSize MaybeV2Size,
+ AssumptionCache *AC,
+ DominatorTree *DT,
+ const AAQueryInfo &AAQI) {
+ if (GEP.VarIndices.size() != 2 || !MaybeV1Size.hasValue() ||
+ !MaybeV2Size.hasValue())
+ return false;
+
+ const uint64_t V1Size = MaybeV1Size.getValue();
+ const uint64_t V2Size = MaybeV2Size.getValue();
+
+ const VariableGEPIndex &Var0 = GEP.VarIndices[0], &Var1 = GEP.VarIndices[1];
+
+ if (Var0.Val.TruncBits != 0 || !Var0.Val.hasSameCastsAs(Var1.Val) ||
+ !Var0.hasNegatedScaleOf(Var1) ||
+ Var0.Val.V->getType() != Var1.Val.V->getType())
+ return false;
+
+ // 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.
+
+ LinearExpression E0 =
+ GetLinearExpression(CastedValue(Var0.Val.V), DL, 0, AC, DT);
+ LinearExpression E1 =
+ GetLinearExpression(CastedValue(Var1.Val.V), DL, 0, AC, DT);
+ if (E0.Scale != E1.Scale || !E0.Val.hasSameCastsAs(E1.Val) ||
+ !isValueEqualInPotentialCycles(E0.Val.V, E1.Val.V, AAQI))
+ 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 = E0.Offset - E1.Offset, 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 + GEP.Offset.abs()) &&
+ MinDiffBytes.uge(V2Size + GEP.Offset.abs());
+}
+
+//===----------------------------------------------------------------------===//
+// BasicAliasAnalysis Pass
+//===----------------------------------------------------------------------===//
+
+AnalysisKey BasicAA::Key;
+
+BasicAAResult BasicAA::run(Function &F, FunctionAnalysisManager &AM) {
+ auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
+ auto &AC = AM.getResult<AssumptionAnalysis>(F);
+ auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
+ return BasicAAResult(F.getDataLayout(), F, TLI, AC, DT);
+}
+
+BasicAAWrapperPass::BasicAAWrapperPass() : FunctionPass(ID) {
+ initializeBasicAAWrapperPassPass(*PassRegistry::getPassRegistry());
+}
+
+char BasicAAWrapperPass::ID = 0;
+
+void BasicAAWrapperPass::anchor() {}
+
+INITIALIZE_PASS_BEGIN(BasicAAWrapperPass, "basic-aa",
+ "Basic Alias Analysis (stateless AA impl)", true, true)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(BasicAAWrapperPass, "basic-aa",
+ "Basic Alias Analysis (stateless AA impl)", true, true)
+
+FunctionPass *llvm::createBasicAAWrapperPass() {
+ return new BasicAAWrapperPass();
+}
+
+bool BasicAAWrapperPass::runOnFunction(Function &F) {
+ auto &ACT = getAnalysis<AssumptionCacheTracker>();
+ auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>();
+ auto &DTWP = getAnalysis<DominatorTreeWrapperPass>();
+
+ Result.reset(new BasicAAResult(F.getDataLayout(), F,
+ TLIWP.getTLI(F), ACT.getAssumptionCache(F),
+ &DTWP.getDomTree()));
+
+ return false;
+}
+
+void BasicAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesAll();
+ AU.addRequiredTransitive<AssumptionCacheTracker>();
+ AU.addRequiredTransitive<DominatorTreeWrapperPass>();
+ AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>();
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-07-10 09:47:26 +0000