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//===--- CodeGenTypes.cpp - TBAA information for LLVM CodeGen -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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 "clang/AST/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Mangle.h"
#include "clang/AST/RecordLayout.h"
#include "clang/Frontend/CodeGenOptions.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"
using namespace clang;
using namespace CodeGen;
CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::Module &M,
const CodeGenOptions &CGO,
const LangOptions &Features, MangleContext &MContext)
: Context(Ctx), 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 (const TagType *TTy = dyn_cast<TagType>(QTy))
return TTy->getDecl()->hasAttr<MayAliasAttr>();
// Typedef types have declarations, and therefore may have attributes.
if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
if (TTy->getDecl()->hasAttr<MayAliasAttr>())
return true;
// Also, their underlying types may have relevant attributes.
return TypeHasMayAlias(TTy->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 (QTy->isReferenceType())
return false;
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);
// 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)) {
// 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 (!Features.CPlusPlus || !ETy->getDecl()->isExternallyVisible())
return getChar();
SmallString<256> OutName;
llvm::raw_svector_ostream Out(OutName);
MContext.mangleTypeName(QualType(ETy, 0), Out);
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 getBaseTypeInfo() into a single function.
if (isValidBaseType(QTy))
return getBaseTypeInfo(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::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>()) {
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);
unsigned idx = 0;
for (RecordDecl::field_iterator i = RD->field_begin(),
e = RD->field_end(); i != e; ++i, ++idx) {
uint64_t Offset = BaseOffset +
Layout.getFieldOffset(idx) / Context.getCharWidth();
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) {
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);
SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
for (FieldDecl *Field : RD->fields()) {
QualType FieldQTy = Field->getType();
llvm::MDNode *TypeNode = isValidBaseType(FieldQTy) ?
getBaseTypeInfo(FieldQTy) : getTypeInfo(FieldQTy);
if (!TypeNode)
return BaseTypeMetadataCache[Ty] = 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.mangleTypeName(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::getBaseTypeInfo(QualType QTy) {
if (!isValidBaseType(QTy))
return nullptr;
const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
if (llvm::MDNode *N = BaseTypeMetadataCache[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 = getBaseTypeInfoHelper(Ty);
return BaseTypeMetadataCache[Ty] = TypeNode;
}
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();
}