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//===------- MicrosoftCXXABI.cpp - AST support for the Microsoft C++ ABI --===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This provides C++ AST support targeting the Microsoft Visual C++
// ABI.
//
//===----------------------------------------------------------------------===//
#include "CXXABI.h"
#include "clang/AST/Attr.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/Type.h"
#include "clang/Basic/TargetInfo.h"
using namespace clang;
namespace {
class MicrosoftCXXABI : public CXXABI {
ASTContext &Context;
public:
MicrosoftCXXABI(ASTContext &Ctx) : Context(Ctx) { }
std::pair<uint64_t, unsigned>
getMemberPointerWidthAndAlign(const MemberPointerType *MPT) const;
CallingConv getDefaultMethodCallConv(bool isVariadic) const {
if (!isVariadic &&
Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86)
return CC_X86ThisCall;
return CC_C;
}
bool isNearlyEmpty(const CXXRecordDecl *RD) const {
// FIXME: Audit the corners
if (!RD->isDynamicClass())
return false;
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
// In the Microsoft ABI, classes can have one or two vtable pointers.
CharUnits PointerSize =
Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
return Layout.getNonVirtualSize() == PointerSize ||
Layout.getNonVirtualSize() == PointerSize * 2;
}
};
}
// getNumBases() seems to only give us the number of direct bases, and not the
// total. This function tells us if we inherit from anybody that uses MI, or if
// we have a non-primary base class, which uses the multiple inheritance model.
static bool usesMultipleInheritanceModel(const CXXRecordDecl *RD) {
while (RD->getNumBases() > 0) {
if (RD->getNumBases() > 1)
return true;
assert(RD->getNumBases() == 1);
const CXXRecordDecl *Base =
RD->bases_begin()->getType()->getAsCXXRecordDecl();
if (RD->isPolymorphic() && !Base->isPolymorphic())
return true;
RD = Base;
}
return false;
}
static MSInheritanceModel MSInheritanceAttrToModel(attr::Kind Kind) {
switch (Kind) {
default: llvm_unreachable("expected MS inheritance attribute");
case attr::SingleInheritance: return MSIM_Single;
case attr::MultipleInheritance: return MSIM_Multiple;
case attr::VirtualInheritance: return MSIM_Virtual;
case attr::UnspecifiedInheritance: return MSIM_Unspecified;
}
}
MSInheritanceModel CXXRecordDecl::getMSInheritanceModel() const {
if (Attr *IA = this->getAttr<MSInheritanceAttr>())
return MSInheritanceAttrToModel(IA->getKind());
// If there was no explicit attribute, the record must be defined already, and
// we can figure out the inheritance model from its other properties.
if (this->getNumVBases() > 0)
return MSIM_Virtual;
if (usesMultipleInheritanceModel(this))
return this->isPolymorphic() ? MSIM_MultiplePolymorphic : MSIM_Multiple;
return this->isPolymorphic() ? MSIM_SinglePolymorphic : MSIM_Single;
}
// Returns the number of pointer and integer slots used to represent a member
// pointer in the MS C++ ABI.
//
// Member function pointers have the following general form; however, fields
// are dropped as permitted (under the MSVC interpretation) by the inheritance
// model of the actual class.
//
// struct {
// // A pointer to the member function to call. If the member function is
// // virtual, this will be a thunk that forwards to the appropriate vftable
// // slot.
// void *FunctionPointerOrVirtualThunk;
//
// // An offset to add to the address of the vbtable pointer after (possibly)
// // selecting the virtual base but before resolving and calling the function.
// // Only needed if the class has any virtual bases or bases at a non-zero
// // offset.
// int NonVirtualBaseAdjustment;
//
// // An offset within the vb-table that selects the virtual base containing
// // the member. Loading from this offset produces a new offset that is
// // added to the address of the vb-table pointer to produce the base.
// int VirtualBaseAdjustmentOffset;
//
// // The offset of the vb-table pointer within the object. Only needed for
// // incomplete types.
// int VBPtrOffset;
// };
static std::pair<unsigned, unsigned>
getMSMemberPointerSlots(const MemberPointerType *MPT) {
const CXXRecordDecl *RD = MPT->getClass()->getAsCXXRecordDecl();
MSInheritanceModel Inheritance = RD->getMSInheritanceModel();
unsigned Ptrs;
unsigned Ints = 0;
if (MPT->isMemberFunctionPointer()) {
// Member function pointers are a struct of a function pointer followed by a
// variable number of ints depending on the inheritance model used. The
// function pointer is a real function if it is non-virtual and a vftable
// slot thunk if it is virtual. The ints select the object base passed for
// the 'this' pointer.
Ptrs = 1; // First slot is always a function pointer.
switch (Inheritance) {
case MSIM_Unspecified: ++Ints; // VBTableOffset
case MSIM_Virtual: ++Ints; // VirtualBaseAdjustmentOffset
case MSIM_MultiplePolymorphic:
case MSIM_Multiple: ++Ints; // NonVirtualBaseAdjustment
case MSIM_SinglePolymorphic:
case MSIM_Single: break; // Nothing
}
} else {
// Data pointers are an aggregate of ints. The first int is an offset
// followed by vbtable-related offsets.
Ptrs = 0;
switch (Inheritance) {
case MSIM_Unspecified: ++Ints; // VBTableOffset
case MSIM_Virtual: ++Ints; // VirtualBaseAdjustmentOffset
case MSIM_MultiplePolymorphic:
case MSIM_Multiple: // Nothing
case MSIM_SinglePolymorphic:
case MSIM_Single: ++Ints; // Field offset
}
}
return std::make_pair(Ptrs, Ints);
}
std::pair<uint64_t, unsigned> MicrosoftCXXABI::getMemberPointerWidthAndAlign(
const MemberPointerType *MPT) const {
const TargetInfo &Target = Context.getTargetInfo();
assert(Target.getTriple().getArch() == llvm::Triple::x86 ||
Target.getTriple().getArch() == llvm::Triple::x86_64);
unsigned Ptrs, Ints;
llvm::tie(Ptrs, Ints) = getMSMemberPointerSlots(MPT);
// The nominal struct is laid out with pointers followed by ints and aligned
// to a pointer width if any are present and an int width otherwise.
unsigned PtrSize = Target.getPointerWidth(0);
unsigned IntSize = Target.getIntWidth();
uint64_t Width = Ptrs * PtrSize + Ints * IntSize;
unsigned Align = Ptrs > 0 ? Target.getPointerAlign(0) : Target.getIntAlign();
Width = llvm::RoundUpToAlignment(Width, Align);
return std::make_pair(Width, Align);
}
CXXABI *clang::CreateMicrosoftCXXABI(ASTContext &Ctx) {
return new MicrosoftCXXABI(Ctx);
}
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