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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/Type.h"
using namespace clang;
using namespace CodeGen;
CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext& VMContext,
const CodeGenOptions &CGO,
const LangOptions &Features, MangleContext &MContext)
: Context(Ctx), CodeGenOpts(CGO), Features(Features), MContext(MContext),
MDHelper(VMContext), Root(0), Char(0) {
}
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)
Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
return Root;
}
// For struct-path aware TBAA, the scalar type has the same format as
// the struct type: name, offset, pointer to another node in the type DAG.
// For scalar TBAA, the scalar type is the same as the scalar tag:
// name and a parent pointer.
llvm::MDNode *CodeGenTBAA::createTBAAScalarType(StringRef Name,
llvm::MDNode *Parent) {
if (CodeGenOpts.StructPathTBAA)
return MDHelper.createTBAAScalarTypeNode(Name, Parent);
else
return MDHelper.createTBAANode(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 = createTBAAScalarType("omnipotent char", getRoot());
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;
}
llvm::MDNode *
CodeGenTBAA::getTBAAInfo(QualType QTy) {
// At -O0 TBAA is not emitted for regular types.
if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing)
return NULL;
// 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();
const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
if (llvm::MDNode *N = MetadataCache[Ty])
return N;
// 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 getTBAAInfo(Context.ShortTy);
case BuiltinType::UInt:
return getTBAAInfo(Context.IntTy);
case BuiltinType::ULong:
return getTBAAInfo(Context.LongTy);
case BuiltinType::ULongLong:
return getTBAAInfo(Context.LongLongTy);
case BuiltinType::UInt128:
return getTBAAInfo(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 MetadataCache[Ty] =
createTBAAScalarType(BTy->getName(Features), getChar());
}
}
// Handle pointers.
// TODO: Implement C++'s type "similarity" and consider dis-"similar"
// pointers distinct.
if (Ty->isPointerType())
return MetadataCache[Ty] = createTBAAScalarType("any pointer",
getChar());
// 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 MetadataCache[Ty] = getChar();
// TODO: This is using the RTTI name. Is there a better way to get
// a unique string for a type?
SmallString<256> OutName;
llvm::raw_svector_ostream Out(OutName);
MContext.mangleCXXRTTIName(QualType(ETy, 0), Out);
Out.flush();
return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
}
// For now, handle any other kind of type conservatively.
return MetadataCache[Ty] = getChar();
}
llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
return createTBAAScalarType("vtable pointer", getRoot());
}
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 *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy);
llvm::MDNode *TBAATag = CodeGenOpts.StructPathTBAA ?
getTBAAScalarTagInfo(TBAAInfo) : TBAAInfo;
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] = NULL;
}
/// Check if the given type can be handled by path-aware TBAA.
static bool isTBAAPathStruct(QualType QTy) {
if (const RecordType *TTy = QTy->getAs<RecordType>()) {
const RecordDecl *RD = TTy->getDecl()->getDefinition();
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::getTBAAStructTypeInfo(QualType QTy) {
const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
assert(isTBAAPathStruct(QTy));
if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
return N;
if (const RecordType *TTy = QTy->getAs<RecordType>()) {
const RecordDecl *RD = TTy->getDecl()->getDefinition();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
SmallVector <std::pair<llvm::MDNode*, uint64_t>, 4> Fields;
unsigned idx = 0;
for (RecordDecl::field_iterator i = RD->field_begin(),
e = RD->field_end(); i != e; ++i, ++idx) {
QualType FieldQTy = i->getType();
llvm::MDNode *FieldNode;
if (isTBAAPathStruct(FieldQTy))
FieldNode = getTBAAStructTypeInfo(FieldQTy);
else
FieldNode = getTBAAInfo(FieldQTy);
if (!FieldNode)
return StructTypeMetadataCache[Ty] = NULL;
Fields.push_back(std::make_pair(
FieldNode, Layout.getFieldOffset(idx) / Context.getCharWidth()));
}
// TODO: This is using the RTTI name. Is there a better way to get
// a unique string for a type?
SmallString<256> OutName;
llvm::raw_svector_ostream Out(OutName);
MContext.mangleCXXRTTIName(QualType(Ty, 0), Out);
Out.flush();
// Create the struct type node with a vector of pairs (offset, type).
return StructTypeMetadataCache[Ty] =
MDHelper.createTBAAStructTypeNode(OutName, Fields);
}
return StructMetadataCache[Ty] = NULL;
}
llvm::MDNode *
CodeGenTBAA::getTBAAStructTagInfo(QualType BaseQTy, llvm::MDNode *AccessNode,
uint64_t Offset) {
if (!CodeGenOpts.StructPathTBAA)
return AccessNode;
const Type *BTy = Context.getCanonicalType(BaseQTy).getTypePtr();
TBAAPathTag PathTag = TBAAPathTag(BTy, AccessNode, Offset);
if (llvm::MDNode *N = StructTagMetadataCache[PathTag])
return N;
llvm::MDNode *BNode = 0;
if (isTBAAPathStruct(BaseQTy))
BNode = getTBAAStructTypeInfo(BaseQTy);
if (!BNode)
return StructTagMetadataCache[PathTag] =
MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
return StructTagMetadataCache[PathTag] =
MDHelper.createTBAAStructTagNode(BNode, AccessNode, Offset);
}
llvm::MDNode *
CodeGenTBAA::getTBAAScalarTagInfo(llvm::MDNode *AccessNode) {
if (llvm::MDNode *N = ScalarTagMetadataCache[AccessNode])
return N;
return ScalarTagMetadataCache[AccessNode] =
MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
}