| //===-- CodeGenTBAA.cpp - TBAA information for LLVM CodeGen ---------------===// |
| // |
| // 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 is the code that manages TBAA information and defines the TBAA policy |
| // for the optimizer to use. Relevant standards text includes: |
| // |
| // C99 6.5p7 |
| // C++ [basic.lval] (p10 in n3126, p15 in some earlier versions) |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "CodeGenTBAA.h" |
| #include "CGRecordLayout.h" |
| #include "CodeGenTypes.h" |
| #include "clang/AST/ASTContext.h" |
| #include "clang/AST/Attr.h" |
| #include "clang/AST/Mangle.h" |
| #include "clang/AST/RecordLayout.h" |
| #include "clang/Basic/CodeGenOptions.h" |
| #include "clang/Basic/TargetInfo.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/LLVMContext.h" |
| #include "llvm/IR/Metadata.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/Support/Debug.h" |
| using namespace clang; |
| using namespace CodeGen; |
| |
| CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, CodeGenTypes &CGTypes, |
| llvm::Module &M, const CodeGenOptions &CGO, |
| const LangOptions &Features, MangleContext &MContext) |
| : Context(Ctx), CGTypes(CGTypes), Module(M), CodeGenOpts(CGO), |
| Features(Features), MContext(MContext), MDHelper(M.getContext()), |
| Root(nullptr), Char(nullptr) {} |
| |
| CodeGenTBAA::~CodeGenTBAA() { |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getRoot() { |
| // Define the root of the tree. This identifies the tree, so that |
| // if our LLVM IR is linked with LLVM IR from a different front-end |
| // (or a different version of this front-end), their TBAA trees will |
| // remain distinct, and the optimizer will treat them conservatively. |
| if (!Root) { |
| if (Features.CPlusPlus) |
| Root = MDHelper.createTBAARoot("Simple C++ TBAA"); |
| else |
| Root = MDHelper.createTBAARoot("Simple C/C++ TBAA"); |
| } |
| |
| return Root; |
| } |
| |
| llvm::MDNode *CodeGenTBAA::createScalarTypeNode(StringRef Name, |
| llvm::MDNode *Parent, |
| uint64_t Size) { |
| if (CodeGenOpts.NewStructPathTBAA) { |
| llvm::Metadata *Id = MDHelper.createString(Name); |
| return MDHelper.createTBAATypeNode(Parent, Size, Id); |
| } |
| return MDHelper.createTBAAScalarTypeNode(Name, Parent); |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getChar() { |
| // Define the root of the tree for user-accessible memory. C and C++ |
| // give special powers to char and certain similar types. However, |
| // these special powers only cover user-accessible memory, and doesn't |
| // include things like vtables. |
| if (!Char) |
| Char = createScalarTypeNode("omnipotent char", getRoot(), /* Size= */ 1); |
| |
| return Char; |
| } |
| |
| static bool TypeHasMayAlias(QualType QTy) { |
| // Tagged types have declarations, and therefore may have attributes. |
| if (auto *TD = QTy->getAsTagDecl()) |
| if (TD->hasAttr<MayAliasAttr>()) |
| return true; |
| |
| // Also look for may_alias as a declaration attribute on a typedef. |
| // FIXME: We should follow GCC and model may_alias as a type attribute |
| // rather than as a declaration attribute. |
| while (auto *TT = QTy->getAs<TypedefType>()) { |
| if (TT->getDecl()->hasAttr<MayAliasAttr>()) |
| return true; |
| QTy = TT->desugar(); |
| } |
| return false; |
| } |
| |
| /// Check if the given type is a valid base type to be used in access tags. |
| static bool isValidBaseType(QualType QTy) { |
| if (const RecordType *TTy = QTy->getAs<RecordType>()) { |
| const RecordDecl *RD = TTy->getDecl()->getDefinition(); |
| // Incomplete types are not valid base access types. |
| if (!RD) |
| return false; |
| if (RD->hasFlexibleArrayMember()) |
| return false; |
| // RD can be struct, union, class, interface or enum. |
| // For now, we only handle struct and class. |
| if (RD->isStruct() || RD->isClass()) |
| return true; |
| } |
| return false; |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) { |
| uint64_t Size = Context.getTypeSizeInChars(Ty).getQuantity(); |
| |
| // Handle builtin types. |
| if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) { |
| switch (BTy->getKind()) { |
| // Character types are special and can alias anything. |
| // In C++, this technically only includes "char" and "unsigned char", |
| // and not "signed char". In C, it includes all three. For now, |
| // the risk of exploiting this detail in C++ seems likely to outweigh |
| // the benefit. |
| case BuiltinType::Char_U: |
| case BuiltinType::Char_S: |
| case BuiltinType::UChar: |
| case BuiltinType::SChar: |
| return getChar(); |
| |
| // Unsigned types can alias their corresponding signed types. |
| case BuiltinType::UShort: |
| return getTypeInfo(Context.ShortTy); |
| case BuiltinType::UInt: |
| return getTypeInfo(Context.IntTy); |
| case BuiltinType::ULong: |
| return getTypeInfo(Context.LongTy); |
| case BuiltinType::ULongLong: |
| return getTypeInfo(Context.LongLongTy); |
| case BuiltinType::UInt128: |
| return getTypeInfo(Context.Int128Ty); |
| |
| case BuiltinType::UShortFract: |
| return getTypeInfo(Context.ShortFractTy); |
| case BuiltinType::UFract: |
| return getTypeInfo(Context.FractTy); |
| case BuiltinType::ULongFract: |
| return getTypeInfo(Context.LongFractTy); |
| |
| case BuiltinType::SatUShortFract: |
| return getTypeInfo(Context.SatShortFractTy); |
| case BuiltinType::SatUFract: |
| return getTypeInfo(Context.SatFractTy); |
| case BuiltinType::SatULongFract: |
| return getTypeInfo(Context.SatLongFractTy); |
| |
| case BuiltinType::UShortAccum: |
| return getTypeInfo(Context.ShortAccumTy); |
| case BuiltinType::UAccum: |
| return getTypeInfo(Context.AccumTy); |
| case BuiltinType::ULongAccum: |
| return getTypeInfo(Context.LongAccumTy); |
| |
| case BuiltinType::SatUShortAccum: |
| return getTypeInfo(Context.SatShortAccumTy); |
| case BuiltinType::SatUAccum: |
| return getTypeInfo(Context.SatAccumTy); |
| case BuiltinType::SatULongAccum: |
| return getTypeInfo(Context.SatLongAccumTy); |
| |
| // Treat all other builtin types as distinct types. This includes |
| // treating wchar_t, char16_t, and char32_t as distinct from their |
| // "underlying types". |
| default: |
| return createScalarTypeNode(BTy->getName(Features), getChar(), Size); |
| } |
| } |
| |
| // C++1z [basic.lval]p10: "If a program attempts to access the stored value of |
| // an object through a glvalue of other than one of the following types the |
| // behavior is undefined: [...] a char, unsigned char, or std::byte type." |
| if (Ty->isStdByteType()) |
| return getChar(); |
| |
| // Handle pointers and references. |
| // TODO: Implement C++'s type "similarity" and consider dis-"similar" |
| // pointers distinct. |
| if (Ty->isPointerType() || Ty->isReferenceType()) |
| return createScalarTypeNode("any pointer", getChar(), Size); |
| |
| // Accesses to arrays are accesses to objects of their element types. |
| if (CodeGenOpts.NewStructPathTBAA && Ty->isArrayType()) |
| return getTypeInfo(cast<ArrayType>(Ty)->getElementType()); |
| |
| // Enum types are distinct types. In C++ they have "underlying types", |
| // however they aren't related for TBAA. |
| if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) { |
| if (!Features.CPlusPlus) |
| return getTypeInfo(ETy->getDecl()->getIntegerType()); |
| |
| // In C++ mode, types have linkage, so we can rely on the ODR and |
| // on their mangled names, if they're external. |
| // TODO: Is there a way to get a program-wide unique name for a |
| // decl with local linkage or no linkage? |
| if (!ETy->getDecl()->isExternallyVisible()) |
| return getChar(); |
| |
| SmallString<256> OutName; |
| llvm::raw_svector_ostream Out(OutName); |
| MContext.mangleCanonicalTypeName(QualType(ETy, 0), Out); |
| return createScalarTypeNode(OutName, getChar(), Size); |
| } |
| |
| if (const auto *EIT = dyn_cast<BitIntType>(Ty)) { |
| SmallString<256> OutName; |
| llvm::raw_svector_ostream Out(OutName); |
| // Don't specify signed/unsigned since integer types can alias despite sign |
| // differences. |
| Out << "_BitInt(" << EIT->getNumBits() << ')'; |
| return createScalarTypeNode(OutName, getChar(), Size); |
| } |
| |
| // For now, handle any other kind of type conservatively. |
| return getChar(); |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getTypeInfo(QualType QTy) { |
| // At -O0 or relaxed aliasing, TBAA is not emitted for regular types. |
| if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing) |
| return nullptr; |
| |
| // If the type has the may_alias attribute (even on a typedef), it is |
| // effectively in the general char alias class. |
| if (TypeHasMayAlias(QTy)) |
| return getChar(); |
| |
| // We need this function to not fall back to returning the "omnipotent char" |
| // type node for aggregate and union types. Otherwise, any dereference of an |
| // aggregate will result into the may-alias access descriptor, meaning all |
| // subsequent accesses to direct and indirect members of that aggregate will |
| // be considered may-alias too. |
| // TODO: Combine getTypeInfo() and getValidBaseTypeInfo() into a single |
| // function. |
| if (isValidBaseType(QTy)) |
| return getValidBaseTypeInfo(QTy); |
| |
| const Type *Ty = Context.getCanonicalType(QTy).getTypePtr(); |
| if (llvm::MDNode *N = MetadataCache[Ty]) |
| return N; |
| |
| // Note that the following helper call is allowed to add new nodes to the |
| // cache, which invalidates all its previously obtained iterators. So we |
| // first generate the node for the type and then add that node to the cache. |
| llvm::MDNode *TypeNode = getTypeInfoHelper(Ty); |
| return MetadataCache[Ty] = TypeNode; |
| } |
| |
| TBAAAccessInfo CodeGenTBAA::getAccessInfo(QualType AccessType) { |
| // Pointee values may have incomplete types, but they shall never be |
| // dereferenced. |
| if (AccessType->isIncompleteType()) |
| return TBAAAccessInfo::getIncompleteInfo(); |
| |
| if (TypeHasMayAlias(AccessType)) |
| return TBAAAccessInfo::getMayAliasInfo(); |
| |
| uint64_t Size = Context.getTypeSizeInChars(AccessType).getQuantity(); |
| return TBAAAccessInfo(getTypeInfo(AccessType), Size); |
| } |
| |
| TBAAAccessInfo CodeGenTBAA::getVTablePtrAccessInfo(llvm::Type *VTablePtrType) { |
| llvm::DataLayout DL(&Module); |
| unsigned Size = DL.getPointerTypeSize(VTablePtrType); |
| return TBAAAccessInfo(createScalarTypeNode("vtable pointer", getRoot(), Size), |
| Size); |
| } |
| |
| bool |
| CodeGenTBAA::CollectFields(uint64_t BaseOffset, |
| QualType QTy, |
| SmallVectorImpl<llvm::MDBuilder::TBAAStructField> & |
| Fields, |
| bool MayAlias) { |
| /* Things not handled yet include: C++ base classes, bitfields, */ |
| |
| if (const RecordType *TTy = QTy->getAs<RecordType>()) { |
| if (TTy->isUnionType()) { |
| uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity(); |
| llvm::MDNode *TBAAType = getChar(); |
| llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size)); |
| Fields.push_back( |
| llvm::MDBuilder::TBAAStructField(BaseOffset, Size, TBAATag)); |
| return true; |
| } |
| const RecordDecl *RD = TTy->getDecl()->getDefinition(); |
| if (RD->hasFlexibleArrayMember()) |
| return false; |
| |
| // TODO: Handle C++ base classes. |
| if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD)) |
| if (Decl->bases_begin() != Decl->bases_end()) |
| return false; |
| |
| const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD); |
| const CGRecordLayout &CGRL = CGTypes.getCGRecordLayout(RD); |
| |
| unsigned idx = 0; |
| for (RecordDecl::field_iterator i = RD->field_begin(), e = RD->field_end(); |
| i != e; ++i, ++idx) { |
| if ((*i)->isZeroSize(Context)) |
| continue; |
| |
| uint64_t Offset = |
| BaseOffset + Layout.getFieldOffset(idx) / Context.getCharWidth(); |
| |
| // Create a single field for consecutive named bitfields using char as |
| // base type. |
| if ((*i)->isBitField()) { |
| const CGBitFieldInfo &Info = CGRL.getBitFieldInfo(*i); |
| // For big endian targets the first bitfield in the consecutive run is |
| // at the most-significant end; see CGRecordLowering::setBitFieldInfo |
| // for more information. |
| bool IsBE = Context.getTargetInfo().isBigEndian(); |
| bool IsFirst = IsBE ? Info.StorageSize - (Info.Offset + Info.Size) == 0 |
| : Info.Offset == 0; |
| if (!IsFirst) |
| continue; |
| unsigned CurrentBitFieldSize = Info.StorageSize; |
| uint64_t Size = |
| llvm::divideCeil(CurrentBitFieldSize, Context.getCharWidth()); |
| llvm::MDNode *TBAAType = getChar(); |
| llvm::MDNode *TBAATag = |
| getAccessTagInfo(TBAAAccessInfo(TBAAType, Size)); |
| Fields.push_back( |
| llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag)); |
| continue; |
| } |
| |
| QualType FieldQTy = i->getType(); |
| if (!CollectFields(Offset, FieldQTy, Fields, |
| MayAlias || TypeHasMayAlias(FieldQTy))) |
| return false; |
| } |
| return true; |
| } |
| |
| /* Otherwise, treat whatever it is as a field. */ |
| uint64_t Offset = BaseOffset; |
| uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity(); |
| llvm::MDNode *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy); |
| llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size)); |
| Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag)); |
| return true; |
| } |
| |
| llvm::MDNode * |
| CodeGenTBAA::getTBAAStructInfo(QualType QTy) { |
| if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing) |
| return nullptr; |
| |
| const Type *Ty = Context.getCanonicalType(QTy).getTypePtr(); |
| |
| if (llvm::MDNode *N = StructMetadataCache[Ty]) |
| return N; |
| |
| SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields; |
| if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy))) |
| return MDHelper.createTBAAStructNode(Fields); |
| |
| // For now, handle any other kind of type conservatively. |
| return StructMetadataCache[Ty] = nullptr; |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getBaseTypeInfoHelper(const Type *Ty) { |
| if (auto *TTy = dyn_cast<RecordType>(Ty)) { |
| const RecordDecl *RD = TTy->getDecl()->getDefinition(); |
| const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD); |
| using TBAAStructField = llvm::MDBuilder::TBAAStructField; |
| SmallVector<TBAAStructField, 4> Fields; |
| if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) { |
| // Handle C++ base classes. Non-virtual bases can treated a kind of |
| // field. Virtual bases are more complex and omitted, but avoid an |
| // incomplete view for NewStructPathTBAA. |
| if (CodeGenOpts.NewStructPathTBAA && CXXRD->getNumVBases() != 0) |
| return nullptr; |
| for (const CXXBaseSpecifier &B : CXXRD->bases()) { |
| if (B.isVirtual()) |
| continue; |
| QualType BaseQTy = B.getType(); |
| const CXXRecordDecl *BaseRD = BaseQTy->getAsCXXRecordDecl(); |
| if (BaseRD->isEmpty()) |
| continue; |
| llvm::MDNode *TypeNode = isValidBaseType(BaseQTy) |
| ? getValidBaseTypeInfo(BaseQTy) |
| : getTypeInfo(BaseQTy); |
| if (!TypeNode) |
| return nullptr; |
| uint64_t Offset = Layout.getBaseClassOffset(BaseRD).getQuantity(); |
| uint64_t Size = |
| Context.getASTRecordLayout(BaseRD).getDataSize().getQuantity(); |
| Fields.push_back( |
| llvm::MDBuilder::TBAAStructField(Offset, Size, TypeNode)); |
| } |
| // The order in which base class subobjects are allocated is unspecified, |
| // so may differ from declaration order. In particular, Itanium ABI will |
| // allocate a primary base first. |
| // Since we exclude empty subobjects, the objects are not overlapping and |
| // their offsets are unique. |
| llvm::sort(Fields, |
| [](const TBAAStructField &A, const TBAAStructField &B) { |
| return A.Offset < B.Offset; |
| }); |
| } |
| for (FieldDecl *Field : RD->fields()) { |
| if (Field->isZeroSize(Context) || Field->isUnnamedBitField()) |
| continue; |
| QualType FieldQTy = Field->getType(); |
| llvm::MDNode *TypeNode = isValidBaseType(FieldQTy) |
| ? getValidBaseTypeInfo(FieldQTy) |
| : getTypeInfo(FieldQTy); |
| if (!TypeNode) |
| return nullptr; |
| |
| uint64_t BitOffset = Layout.getFieldOffset(Field->getFieldIndex()); |
| uint64_t Offset = Context.toCharUnitsFromBits(BitOffset).getQuantity(); |
| uint64_t Size = Context.getTypeSizeInChars(FieldQTy).getQuantity(); |
| Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, |
| TypeNode)); |
| } |
| |
| SmallString<256> OutName; |
| if (Features.CPlusPlus) { |
| // Don't use the mangler for C code. |
| llvm::raw_svector_ostream Out(OutName); |
| MContext.mangleCanonicalTypeName(QualType(Ty, 0), Out); |
| } else { |
| OutName = RD->getName(); |
| } |
| |
| if (CodeGenOpts.NewStructPathTBAA) { |
| llvm::MDNode *Parent = getChar(); |
| uint64_t Size = Context.getTypeSizeInChars(Ty).getQuantity(); |
| llvm::Metadata *Id = MDHelper.createString(OutName); |
| return MDHelper.createTBAATypeNode(Parent, Size, Id, Fields); |
| } |
| |
| // Create the struct type node with a vector of pairs (offset, type). |
| SmallVector<std::pair<llvm::MDNode*, uint64_t>, 4> OffsetsAndTypes; |
| for (const auto &Field : Fields) |
| OffsetsAndTypes.push_back(std::make_pair(Field.Type, Field.Offset)); |
| return MDHelper.createTBAAStructTypeNode(OutName, OffsetsAndTypes); |
| } |
| |
| return nullptr; |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getValidBaseTypeInfo(QualType QTy) { |
| assert(isValidBaseType(QTy) && "Must be a valid base type"); |
| |
| const Type *Ty = Context.getCanonicalType(QTy).getTypePtr(); |
| |
| // nullptr is a valid value in the cache, so use find rather than [] |
| auto I = BaseTypeMetadataCache.find(Ty); |
| if (I != BaseTypeMetadataCache.end()) |
| return I->second; |
| |
| // First calculate the metadata, before recomputing the insertion point, as |
| // the helper can recursively call us. |
| llvm::MDNode *TypeNode = getBaseTypeInfoHelper(Ty); |
| LLVM_ATTRIBUTE_UNUSED auto inserted = |
| BaseTypeMetadataCache.insert({Ty, TypeNode}); |
| assert(inserted.second && "BaseType metadata was already inserted"); |
| |
| return TypeNode; |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getBaseTypeInfo(QualType QTy) { |
| return isValidBaseType(QTy) ? getValidBaseTypeInfo(QTy) : nullptr; |
| } |
| |
| llvm::MDNode *CodeGenTBAA::getAccessTagInfo(TBAAAccessInfo Info) { |
| assert(!Info.isIncomplete() && "Access to an object of an incomplete type!"); |
| |
| if (Info.isMayAlias()) |
| Info = TBAAAccessInfo(getChar(), Info.Size); |
| |
| if (!Info.AccessType) |
| return nullptr; |
| |
| if (!CodeGenOpts.StructPathTBAA) |
| Info = TBAAAccessInfo(Info.AccessType, Info.Size); |
| |
| llvm::MDNode *&N = AccessTagMetadataCache[Info]; |
| if (N) |
| return N; |
| |
| if (!Info.BaseType) { |
| Info.BaseType = Info.AccessType; |
| assert(!Info.Offset && "Nonzero offset for an access with no base type!"); |
| } |
| if (CodeGenOpts.NewStructPathTBAA) { |
| return N = MDHelper.createTBAAAccessTag(Info.BaseType, Info.AccessType, |
| Info.Offset, Info.Size); |
| } |
| return N = MDHelper.createTBAAStructTagNode(Info.BaseType, Info.AccessType, |
| Info.Offset); |
| } |
| |
| TBAAAccessInfo CodeGenTBAA::mergeTBAAInfoForCast(TBAAAccessInfo SourceInfo, |
| TBAAAccessInfo TargetInfo) { |
| if (SourceInfo.isMayAlias() || TargetInfo.isMayAlias()) |
| return TBAAAccessInfo::getMayAliasInfo(); |
| return TargetInfo; |
| } |
| |
| TBAAAccessInfo |
| CodeGenTBAA::mergeTBAAInfoForConditionalOperator(TBAAAccessInfo InfoA, |
| TBAAAccessInfo InfoB) { |
| if (InfoA == InfoB) |
| return InfoA; |
| |
| if (!InfoA || !InfoB) |
| return TBAAAccessInfo(); |
| |
| if (InfoA.isMayAlias() || InfoB.isMayAlias()) |
| return TBAAAccessInfo::getMayAliasInfo(); |
| |
| // TODO: Implement the rest of the logic here. For example, two accesses |
| // with same final access types result in an access to an object of that final |
| // access type regardless of their base types. |
| return TBAAAccessInfo::getMayAliasInfo(); |
| } |
| |
| TBAAAccessInfo |
| CodeGenTBAA::mergeTBAAInfoForMemoryTransfer(TBAAAccessInfo DestInfo, |
| TBAAAccessInfo SrcInfo) { |
| if (DestInfo == SrcInfo) |
| return DestInfo; |
| |
| if (!DestInfo || !SrcInfo) |
| return TBAAAccessInfo(); |
| |
| if (DestInfo.isMayAlias() || SrcInfo.isMayAlias()) |
| return TBAAAccessInfo::getMayAliasInfo(); |
| |
| // TODO: Implement the rest of the logic here. For example, two accesses |
| // with same final access types result in an access to an object of that final |
| // access type regardless of their base types. |
| return TBAAAccessInfo::getMayAliasInfo(); |
| } |
