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llvm-project/clang/lib/CodeGen/CodeGenTBAA.cpp
Bruno De Fraine 458b1e9d2c
[TBAA] Refine pointer-tbaa for void pointers by pointer depth (#126047) 
Commit 77d3f8a avoids distinct tags for any pointers where the ultimate
pointee type is `void`, to solve breakage in real-world code that uses
(indirections to) `void*` for polymorphism over different pointer types.

While this matches the TBAA implementation in GCC, this patch implements
a refinement that distinguishes void pointers by pointer depth, as
described in the "strict aliasing" documentation included in the
aforementioned commit:
> `void*` is permitted to alias any pointer type, `void**` is permitted
> to alias any pointer to pointer type, and so on.

For example, `void**` is no longer considered to alias `int*` in this
refinement, but it remains possible to use `void**` for polymorphism
over pointers to pointers.
2025-02-20 16:06:56 +04:00

686 lines
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//===-- 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 "ABIInfoImpl.h"
#include "CGCXXABI.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/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)
: Context(Ctx), CGTypes(CGTypes), Module(M), CodeGenOpts(CGO),
Features(Features),
MangleCtx(ItaniumMangleContext::create(Ctx, Ctx.getDiagnostics())),
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;
}
llvm::MDNode *CodeGenTBAA::getAnyPtr(unsigned PtrDepth) {
assert(PtrDepth >= 1 && "Pointer must have some depth");
// Populate at least PtrDepth elements in AnyPtrs. These are the type nodes
// for "any" pointers of increasing pointer depth, and are organized in the
// hierarchy: any pointer <- any p2 pointer <- any p3 pointer <- ...
//
// Note that AnyPtrs[Idx] is actually the node for pointer depth (Idx+1),
// since there is no node for pointer depth 0.
//
// These "any" pointer type nodes are used in pointer TBAA. The type node of
// a concrete pointer type has the "any" pointer type node of appropriate
// pointer depth as its parent. The "any" pointer type nodes are also used
// directly for accesses to void pointers, or to specific pointers that we
// conservatively do not distinguish in pointer TBAA (e.g. pointers to
// members). Essentially, this establishes that e.g. void** can alias with
// any type that can unify with T**, ignoring things like qualifiers. Here, T
// is a variable that represents an arbitrary type, including pointer types.
// As such, each depth is naturally a subtype of the previous depth, and thus
// transitively of all previous depths.
if (AnyPtrs.size() < PtrDepth) {
AnyPtrs.reserve(PtrDepth);
auto Size = Module.getDataLayout().getPointerSize();
// Populate first element.
if (AnyPtrs.empty())
AnyPtrs.push_back(createScalarTypeNode("any pointer", getChar(), Size));
// Populate further elements.
for (size_t Idx = AnyPtrs.size(); Idx < PtrDepth; ++Idx) {
auto Name = ("any p" + llvm::Twine(Idx + 1) + " pointer").str();
AnyPtrs.push_back(createScalarTypeNode(Name, AnyPtrs[Idx - 1], Size));
}
}
return AnyPtrs[PtrDepth - 1];
}
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.
//
// C has a very strict rule for pointer aliasing. C23 6.7.6.1p2:
// For two pointer types to be compatible, both shall be identically
// qualified and both shall be pointers to compatible types.
//
// This rule is impractically strict; we want to at least ignore CVR
// qualifiers. Distinguishing by CVR qualifiers would make it UB to
// e.g. cast a `char **` to `const char * const *` and dereference it,
// which is too common and useful to invalidate. C++'s similar types
// rule permits qualifier differences in these nested positions; in fact,
// C++ even allows that cast as an implicit conversion.
//
// Other qualifiers could theoretically be distinguished, especially if
// they involve a significant representation difference. We don't
// currently do so, however.
if (Ty->isPointerType() || Ty->isReferenceType()) {
if (!CodeGenOpts.PointerTBAA)
return getAnyPtr();
// C++ [basic.lval]p11 permits objects to accessed through an l-value of
// similar type. Two types are similar under C++ [conv.qual]p2 if the
// decomposition of the types into pointers, member pointers, and arrays has
// the same structure when ignoring cv-qualifiers at each level of the
// decomposition. Meanwhile, C makes T(*)[] and T(*)[N] compatible, which
// would really complicate any attempt to distinguish pointers to arrays by
// their bounds. It's simpler, and much easier to explain to users, to
// simply treat all pointers to arrays as pointers to their element type for
// aliasing purposes. So when creating a TBAA tag for a pointer type, we
// recursively ignore both qualifiers and array types when decomposing the
// pointee type. The only meaningful remaining structure is the number of
// pointer types we encountered along the way, so we just produce the tag
// "p<depth> <base type tag>". If we do find a member pointer type, for now
// we just conservatively bail out with AnyPtr (below) rather than trying to
// create a tag that honors the similar-type rules while still
// distinguishing different kinds of member pointer.
unsigned PtrDepth = 0;
do {
PtrDepth++;
Ty = Ty->getPointeeType()->getBaseElementTypeUnsafe();
} while (Ty->isPointerType());
// While there are no special rules in the standards regarding void pointers
// and strict aliasing, emitting distinct tags for void pointers break some
// common idioms and there is no good alternative to re-write the code
// without strict-aliasing violations.
if (Ty->isVoidType())
return getAnyPtr(PtrDepth);
assert(!isa<VariableArrayType>(Ty));
// When the underlying type is a builtin type, we compute the pointee type
// string recursively, which is implicitly more forgiving than the standards
// require. Effectively, we are turning the question "are these types
// compatible/similar" into "are accesses to these types allowed to alias".
// In both C and C++, the latter question has special carve-outs for
// signedness mismatches that only apply at the top level. As a result, we
// are allowing e.g. `int *` l-values to access `unsigned *` objects.
SmallString<256> TyName;
if (isa<BuiltinType>(Ty)) {
llvm::MDNode *ScalarMD = getTypeInfoHelper(Ty);
StringRef Name =
cast<llvm::MDString>(
ScalarMD->getOperand(CodeGenOpts.NewStructPathTBAA ? 2 : 0))
->getString();
TyName = Name;
} else {
// Be conservative if the type isn't a RecordType. We are specifically
// required to do this for member pointers until we implement the
// similar-types rule.
const auto *RT = Ty->getAs<RecordType>();
if (!RT)
return getAnyPtr(PtrDepth);
// For unnamed structs or unions C's compatible types rule applies. Two
// compatible types in different compilation units can have different
// mangled names, meaning the metadata emitted below would incorrectly
// mark them as no-alias. Use AnyPtr for such types in both C and C++, as
// C and C++ types may be visible when doing LTO.
//
// Note that using AnyPtr is overly conservative. We could summarize the
// members of the type, as per the C compatibility rule in the future.
// This also covers anonymous structs and unions, which have a different
// compatibility rule, but it doesn't matter because you can never have a
// pointer to an anonymous struct or union.
if (!RT->getDecl()->getDeclName())
return getAnyPtr(PtrDepth);
// For non-builtin types use the mangled name of the canonical type.
llvm::raw_svector_ostream TyOut(TyName);
MangleCtx->mangleCanonicalTypeName(QualType(Ty, 0), TyOut);
}
SmallString<256> OutName("p");
OutName += std::to_string(PtrDepth);
OutName += " ";
OutName += TyName;
return createScalarTypeNode(OutName, getAnyPtr(PtrDepth), 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);
CGTypes.getCXXABI().getMangleContext().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 (unless
// we're running TypeSanitizer).
if (!Features.Sanitize.has(SanitizerKind::Type) &&
(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) {
const llvm::DataLayout &DL = Module.getDataLayout();
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 (isEmptyFieldForLayout(Context, *i))
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);
CGTypes.getCXXABI().getMangleContext().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();
}
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