C++ CharUnits::RoundUpToAlignment方法代码示例

void CGRecordLowering::insertPadding() {
  std::vector<std::pair<CharUnits, CharUnits> > Padding;
  CharUnits Size = CharUnits::Zero();
  for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
                                               MemberEnd = Members.end();
       Member != MemberEnd; ++Member) {
    if (!Member->Data)
      continue;
    CharUnits Offset = Member->Offset;
    assert(Offset >= Size);
    // Insert padding if we need to.
    if (Offset != Size.RoundUpToAlignment(Packed ? CharUnits::One() :
                                          getAlignment(Member->Data)))
      Padding.push_back(std::make_pair(Size, Offset - Size));
    Size = Offset + getSize(Member->Data);
  }
  if (Padding.empty())
    return;
  // Add the padding to the Members list and sort it.
  for (std::vector<std::pair<CharUnits, CharUnits> >::const_iterator
        Pad = Padding.begin(), PadEnd = Padding.end();
        Pad != PadEnd; ++Pad)
    Members.push_back(StorageInfo(Pad->first, getByteArrayType(Pad->second)));
  std::stable_sort(Members.begin(), Members.end());
}

bool
CGRecordLayoutBuilder::ComputeNonVirtualBaseType(const CXXRecordDecl *RD) {
  const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(RD);

  CharUnits NonVirtualSize  = Layout.getNonVirtualSize();
  CharUnits NonVirtualAlign = Layout.getNonVirtualAlign();
  CharUnits AlignedNonVirtualTypeSize =
    NonVirtualSize.RoundUpToAlignment(NonVirtualAlign);
  
  // First check if we can use the same fields as for the complete class.
  CharUnits RecordSize = Layout.getSize();
  if (AlignedNonVirtualTypeSize == RecordSize)
    return true;

  // Check if we need padding.
  CharUnits AlignedNextFieldOffset =
    NextFieldOffset.RoundUpToAlignment(getAlignmentAsLLVMStruct());

  if (AlignedNextFieldOffset > AlignedNonVirtualTypeSize) {
    assert(!Packed && "cannot layout even as packed struct");
    return false; // Needs packing.
  }

  bool needsPadding = (AlignedNonVirtualTypeSize != AlignedNextFieldOffset);
  if (needsPadding) {
    CharUnits NumBytes = AlignedNonVirtualTypeSize - AlignedNextFieldOffset;
    FieldTypes.push_back(getByteArrayType(NumBytes));
  }
  
  BaseSubobjectType = llvm::StructType::create(Types.getLLVMContext(),
                                               FieldTypes, "", Packed);
  Types.addRecordTypeName(RD, BaseSubobjectType, ".base");

  // Pull the padding back off.
  if (needsPadding)
    FieldTypes.pop_back();

  return true;
}

CGRecordLayout *CodeGenTypes::ComputeRecordLayout(const RecordDecl *D,
                                                  llvm::StructType *Ty) {
  CGRecordLayoutBuilder Builder(*this);

  Builder.Layout(D);

  Ty->setBody(Builder.FieldTypes, Builder.Packed);

  // If we're in C++, compute the base subobject type.
  llvm::StructType *BaseTy = 0;
  if (isa<CXXRecordDecl>(D) && !D->isUnion()) {
    BaseTy = Builder.BaseSubobjectType;
    if (!BaseTy) BaseTy = Ty;
  }

  CGRecordLayout *RL =
    new CGRecordLayout(Ty, BaseTy, Builder.IsZeroInitializable,
                       Builder.IsZeroInitializableAsBase);

  RL->NonVirtualBases.swap(Builder.NonVirtualBases);
  RL->CompleteObjectVirtualBases.swap(Builder.VirtualBases);

  // Add all the field numbers.
  RL->FieldInfo.swap(Builder.Fields);

  // Add bitfield info.
  RL->BitFields.swap(Builder.BitFields);

  // Dump the layout, if requested.
  if (getContext().getLangOpts().DumpRecordLayouts) {
    llvm::outs() << "\n*** Dumping IRgen Record Layout\n";
    llvm::outs() << "Record: ";
    D->dump(llvm::outs());
    llvm::outs() << "\nLayout: ";
    RL->print(llvm::outs());
  }

#ifndef NDEBUG
  // Verify that the computed LLVM struct size matches the AST layout size.
  const ASTRecordLayout &Layout = getContext().getASTRecordLayout(D);

  uint64_t TypeSizeInBits = getContext().toBits(Layout.getSize());
  assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) &&
         "Type size mismatch!");

  if (BaseTy) {
    CharUnits NonVirtualSize  = Layout.getNonVirtualSize();
    CharUnits NonVirtualAlign = Layout.getNonVirtualAlign();
    CharUnits AlignedNonVirtualTypeSize = 
      NonVirtualSize.RoundUpToAlignment(NonVirtualAlign);

    uint64_t AlignedNonVirtualTypeSizeInBits = 
      getContext().toBits(AlignedNonVirtualTypeSize);

    assert(AlignedNonVirtualTypeSizeInBits == 
           getDataLayout().getTypeAllocSizeInBits(BaseTy) &&
           "Type size mismatch!");
  }
                                     
  // Verify that the LLVM and AST field offsets agree.
  llvm::StructType *ST =
    dyn_cast<llvm::StructType>(RL->getLLVMType());
  const llvm::StructLayout *SL = getDataLayout().getStructLayout(ST);

  const ASTRecordLayout &AST_RL = getContext().getASTRecordLayout(D);
  RecordDecl::field_iterator it = D->field_begin();
  for (unsigned i = 0, e = AST_RL.getFieldCount(); i != e; ++i, ++it) {
    const FieldDecl *FD = *it;

    // For non-bit-fields, just check that the LLVM struct offset matches the
    // AST offset.
    if (!FD->isBitField()) {
      unsigned FieldNo = RL->getLLVMFieldNo(FD);
      assert(AST_RL.getFieldOffset(i) == SL->getElementOffsetInBits(FieldNo) &&
             "Invalid field offset!");
      continue;
    }
    
    // Ignore unnamed bit-fields.
    if (!FD->getDeclName())
      continue;

    // Don't inspect zero-length bitfields.
    if (FD->getBitWidthValue(getContext()) == 0)
      continue;

    const CGBitFieldInfo &Info = RL->getBitFieldInfo(FD);
    llvm::Type *ElementTy = ST->getTypeAtIndex(RL->getLLVMFieldNo(FD));

    // Unions have overlapping elements dictating their layout, but for
    // non-unions we can verify that this section of the layout is the exact
    // expected size.
    if (D->isUnion()) {
      // For unions we verify that the start is zero and the size
      // is in-bounds. However, on BE systems, the offset may be non-zero, but
      // the size + offset should match the storage size in that case as it
      // "starts" at the back.
      if (getDataLayout().isBigEndian())
        assert(static_cast<unsigned>(Info.Offset + Info.Size) ==
               Info.StorageSize &&
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