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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/Mangle.h"
#include "clang/Frontend/CodeGenOptions.h"
#include "llvm/LLVMContext.h"
#include "llvm/Metadata.h"
#include "llvm/Constants.h"
#include "llvm/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;
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 = MDHelper.createTBAANode("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".
return MetadataCache[Ty] =
MDHelper.createTBAANode(BTy->getName(Features), getChar());
// Handle pointers.
// TODO: Implement C++'s type "similarity" and consider dis-"similar"
// pointers distinct.
if (Ty->isPointerType())
return MetadataCache[Ty] = MDHelper.createTBAANode("any pointer",
// 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, two anonymous enums are compatible iff their members
// are the same -- see C99 6.2.7p1. For now, be conservative. We could
// theoretically implement this by combining information about all the
// members into a single identifying MDNode.
if (!Features.CPlusPlus &&
return MetadataCache[Ty] = getChar();
// 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()->getLinkage() != ExternalLinkage)
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);
return MetadataCache[Ty] = MDHelper.createTBAANode(OutName, getChar());
// For now, handle any other kind of type conservatively.
return MetadataCache[Ty] = getChar();
llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
return MDHelper.createTBAANode("vtable pointer", getRoot());