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//===------- ItaniumCXXABI.cpp - AST support for the Itanium C++ ABI ------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This provides C++ AST support targeting the Itanium C++ ABI, which is
// documented at:
// It also supports the closely-related ARM C++ ABI, documented at:
#include "CXXABI.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/Mangle.h"
#include "clang/AST/MangleNumberingContext.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/Type.h"
#include "clang/Basic/TargetInfo.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/iterator.h"
using namespace clang;
namespace {
/// According to Itanium C++ ABI 5.1.2:
/// the name of an anonymous union is considered to be
/// the name of the first named data member found by a pre-order,
/// depth-first, declaration-order walk of the data members of
/// the anonymous union.
/// If there is no such data member (i.e., if all of the data members
/// in the union are unnamed), then there is no way for a program to
/// refer to the anonymous union, and there is therefore no need to mangle its name.
/// Returns the name of anonymous union VarDecl or nullptr if it is not found.
static const IdentifierInfo *findAnonymousUnionVarDeclName(const VarDecl& VD) {
const RecordType *RT = VD.getType()->getAs<RecordType>();
assert(RT && "type of VarDecl is expected to be RecordType.");
assert(RT->getDecl()->isUnion() && "RecordType is expected to be a union.");
if (const FieldDecl *FD = RT->getDecl()->findFirstNamedDataMember()) {
return FD->getIdentifier();
return nullptr;
/// The name of a decomposition declaration.
struct DecompositionDeclName {
using BindingArray = ArrayRef<const BindingDecl*>;
/// Representative example of a set of bindings with these names.
BindingArray Bindings;
/// Iterators over the sequence of identifiers in the name.
struct Iterator
: llvm::iterator_adaptor_base<Iterator, BindingArray::const_iterator,
const IdentifierInfo *> {
Iterator(BindingArray::const_iterator It) : iterator_adaptor_base(It) {}
const IdentifierInfo *operator*() const {
return (*this->I)->getIdentifier();
Iterator begin() const { return Iterator(Bindings.begin()); }
Iterator end() const { return Iterator(Bindings.end()); }
namespace llvm {
template<typename T> bool isDenseMapKeyEmpty(T V) {
return llvm::DenseMapInfo<T>::isEqual(
V, llvm::DenseMapInfo<T>::getEmptyKey());
template<typename T> bool isDenseMapKeyTombstone(T V) {
return llvm::DenseMapInfo<T>::isEqual(
V, llvm::DenseMapInfo<T>::getTombstoneKey());
template<typename T>
Optional<bool> areDenseMapKeysEqualSpecialValues(T LHS, T RHS) {
bool LHSEmpty = isDenseMapKeyEmpty(LHS);
bool RHSEmpty = isDenseMapKeyEmpty(RHS);
if (LHSEmpty || RHSEmpty)
return LHSEmpty && RHSEmpty;
bool LHSTombstone = isDenseMapKeyTombstone(LHS);
bool RHSTombstone = isDenseMapKeyTombstone(RHS);
if (LHSTombstone || RHSTombstone)
return LHSTombstone && RHSTombstone;
return None;
struct DenseMapInfo<DecompositionDeclName> {
using ArrayInfo = llvm::DenseMapInfo<ArrayRef<const BindingDecl*>>;
static DecompositionDeclName getEmptyKey() {
return {ArrayInfo::getEmptyKey()};
static DecompositionDeclName getTombstoneKey() {
return {ArrayInfo::getTombstoneKey()};
static unsigned getHashValue(DecompositionDeclName Key) {
assert(!isEqual(Key, getEmptyKey()) && !isEqual(Key, getTombstoneKey()));
return llvm::hash_combine_range(Key.begin(), Key.end());
static bool isEqual(DecompositionDeclName LHS, DecompositionDeclName RHS) {
if (Optional<bool> Result = areDenseMapKeysEqualSpecialValues(
LHS.Bindings, RHS.Bindings))
return *Result;
return LHS.Bindings.size() == RHS.Bindings.size() &&
std::equal(LHS.begin(), LHS.end(), RHS.begin());
namespace {
/// Keeps track of the mangled names of lambda expressions and block
/// literals within a particular context.
class ItaniumNumberingContext : public MangleNumberingContext {
ItaniumMangleContext *Mangler;
llvm::StringMap<unsigned> LambdaManglingNumbers;
unsigned BlockManglingNumber = 0;
llvm::DenseMap<const IdentifierInfo *, unsigned> VarManglingNumbers;
llvm::DenseMap<const IdentifierInfo *, unsigned> TagManglingNumbers;
llvm::DenseMap<DecompositionDeclName, unsigned>
ItaniumNumberingContext(ItaniumMangleContext *Mangler) : Mangler(Mangler) {}
unsigned getManglingNumber(const CXXMethodDecl *CallOperator) override {
const CXXRecordDecl *Lambda = CallOperator->getParent();
// Computation of the <lambda-sig> is non-trivial and subtle. Rather than
// duplicating it here, just mangle the <lambda-sig> directly.
llvm::SmallString<128> LambdaSig;
llvm::raw_svector_ostream Out(LambdaSig);
Mangler->mangleLambdaSig(Lambda, Out);
return ++LambdaManglingNumbers[LambdaSig];
unsigned getManglingNumber(const BlockDecl *BD) override {
return ++BlockManglingNumber;
unsigned getStaticLocalNumber(const VarDecl *VD) override {
return 0;
/// Variable decls are numbered by identifier.
unsigned getManglingNumber(const VarDecl *VD, unsigned) override {
if (auto *DD = dyn_cast<DecompositionDecl>(VD)) {
DecompositionDeclName Name{DD->bindings()};
return ++DecompsitionDeclManglingNumbers[Name];
const IdentifierInfo *Identifier = VD->getIdentifier();
if (!Identifier) {
// VarDecl without an identifier represents an anonymous union
// declaration.
Identifier = findAnonymousUnionVarDeclName(*VD);
return ++VarManglingNumbers[Identifier];
unsigned getManglingNumber(const TagDecl *TD, unsigned) override {
return ++TagManglingNumbers[TD->getIdentifier()];
class ItaniumCXXABI : public CXXABI {
std::unique_ptr<MangleContext> Mangler;
ASTContext &Context;
ItaniumCXXABI(ASTContext &Ctx)
: Mangler(Ctx.createMangleContext()), Context(Ctx) {}
getMemberPointerInfo(const MemberPointerType *MPT) const override {
const TargetInfo &Target = Context.getTargetInfo();
TargetInfo::IntType PtrDiff = Target.getPtrDiffType(0);
MemberPointerInfo MPI;
MPI.Width = Target.getTypeWidth(PtrDiff);
MPI.Align = Target.getTypeAlign(PtrDiff);
MPI.HasPadding = false;
if (MPT->isMemberFunctionPointer())
MPI.Width *= 2;
return MPI;
CallingConv getDefaultMethodCallConv(bool isVariadic) const override {
const llvm::Triple &T = Context.getTargetInfo().getTriple();
if (!isVariadic && T.isWindowsGNUEnvironment() &&
T.getArch() == llvm::Triple::x86)
return CC_X86ThisCall;
return Context.getTargetInfo().getDefaultCallingConv();
// We cheat and just check that the class has a vtable pointer, and that it's
// only big enough to have a vtable pointer and nothing more (or less).
bool isNearlyEmpty(const CXXRecordDecl *RD) const override {
// Check that the class has a vtable pointer.
if (!RD->isDynamicClass())
return false;
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
CharUnits PointerSize =
return Layout.getNonVirtualSize() == PointerSize;
const CXXConstructorDecl *
getCopyConstructorForExceptionObject(CXXRecordDecl *RD) override {
return nullptr;
void addCopyConstructorForExceptionObject(CXXRecordDecl *RD,
CXXConstructorDecl *CD) override {}
void addTypedefNameForUnnamedTagDecl(TagDecl *TD,
TypedefNameDecl *DD) override {}
TypedefNameDecl *getTypedefNameForUnnamedTagDecl(const TagDecl *TD) override {
return nullptr;
void addDeclaratorForUnnamedTagDecl(TagDecl *TD,
DeclaratorDecl *DD) override {}
DeclaratorDecl *getDeclaratorForUnnamedTagDecl(const TagDecl *TD) override {
return nullptr;
createMangleNumberingContext() const override {
return std::make_unique<ItaniumNumberingContext>(
CXXABI *clang::CreateItaniumCXXABI(ASTContext &Ctx) {
return new ItaniumCXXABI(Ctx);