llvm-project/clang/lib/AST/MicrosoftCXXABI.cpp

//===------- 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/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/MangleNumberingContext.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/Type.h"
#include "clang/Basic/TargetInfo.h"

using namespace clang;

namespace {

/// \brief Numbers things which need to correspond across multiple TUs.
/// Typically these are things like static locals, lambdas, or blocks.
class MicrosoftNumberingContext : public MangleNumberingContext {
public:
  unsigned getManglingNumber(const VarDecl *VD,
                             unsigned MSLocalManglingNumber) override {
    return MSLocalManglingNumber;
  }

  unsigned getManglingNumber(const TagDecl *TD,
                             unsigned MSLocalManglingNumber) override {
    return MSLocalManglingNumber;
  }
};

class MicrosoftCXXABI : public CXXABI {
  ASTContext &Context;
public:
  MicrosoftCXXABI(ASTContext &Ctx) : Context(Ctx) { }

  std::pair<uint64_t, unsigned>
  getMemberPointerWidthAndAlign(const MemberPointerType *MPT) const override;

  CallingConv getDefaultMethodCallConv(bool isVariadic) const override {
    if (!isVariadic &&
        Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86)
      return CC_X86ThisCall;
    return CC_C;
  }

  bool isNearlyEmpty(const CXXRecordDecl *RD) const override {
    // 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;
  }    

  MangleNumberingContext *createMangleNumberingContext() const override {
    return new MicrosoftNumberingContext();
  }
};
}

// 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;
}

MSInheritanceAttr::Spelling CXXRecordDecl::calculateInheritanceModel() const {
  if (!hasDefinition() || isParsingBaseSpecifiers())
    return MSInheritanceAttr::Keyword_unspecified_inheritance;
  if (getNumVBases() > 0)
    return MSInheritanceAttr::Keyword_virtual_inheritance;
  if (usesMultipleInheritanceModel(this))
    return MSInheritanceAttr::Keyword_multiple_inheritance;
  return MSInheritanceAttr::Keyword_single_inheritance;
}

MSInheritanceAttr::Spelling
CXXRecordDecl::getMSInheritanceModel() const {
  MSInheritanceAttr *IA = getAttr<MSInheritanceAttr>();
  assert(IA && "Expected MSInheritanceAttr on the CXXRecordDecl!");
  return IA->getSemanticSpelling();
}

MSVtorDispAttr::Mode CXXRecordDecl::getMSVtorDispMode() const {
  if (MSVtorDispAttr *VDA = getAttr<MSVtorDispAttr>())
    return VDA->getVtorDispMode();
  return MSVtorDispAttr::Mode(getASTContext().getLangOpts().VtorDispMode);
}

// 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;
//
//     // The offset of the vb-table pointer within the object.  Only needed for
//     // incomplete types.
//     int VBPtrOffset;
//
//     // 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;
//   };
static std::pair<unsigned, unsigned>
getMSMemberPointerSlots(const MemberPointerType *MPT) {
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();
  unsigned Ptrs = 0;
  unsigned Ints = 0;
  if (MPT->isMemberFunctionPointer())
    Ptrs = 1;
  else
    Ints = 1;
  if (MSInheritanceAttr::hasNVOffsetField(MPT->isMemberFunctionPointer(),
                                          Inheritance))
    Ints++;
  if (MSInheritanceAttr::hasVBPtrOffsetField(Inheritance))
    Ints++;
  if (MSInheritanceAttr::hasVBTableOffsetField(Inheritance))
    Ints++;
  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;
  std::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;

  // When MSVC does x86_32 record layout, it aligns aggregate member pointers to
  // 8 bytes.  However, __alignof usually returns 4 for data memptrs and 8 for
  // function memptrs.
  if (Ptrs + Ints > 1 && Target.getTriple().getArch() == llvm::Triple::x86)
    Align = 8 * 8;
  else if (Ptrs)
    Align = Target.getPointerAlign(0);
  else
    Align = Target.getIntAlign();

  if (Target.getTriple().getArch() == llvm::Triple::x86_64)
    Width = llvm::RoundUpToAlignment(Width, Align);
  return std::make_pair(Width, Align);
}

CXXABI *clang::CreateMicrosoftCXXABI(ASTContext &Ctx) {
  return new MicrosoftCXXABI(Ctx);
}