C++ recorddecl::field_iterator类代码示例

static bool isCallbackArg(SVal V, QualType T) {
  // If the parameter is 0, it's harmless.
  if (V.isZeroConstant())
    return false;

  // If a parameter is a block or a callback, assume it can modify pointer.
  if (T->isBlockPointerType() ||
      T->isFunctionPointerType() ||
      T->isObjCSelType())
    return true;

  // Check if a callback is passed inside a struct (for both, struct passed by
  // reference and by value). Dig just one level into the struct for now.

  if (isa<PointerType>(T) || isa<ReferenceType>(T))
    T = T->getPointeeType();

  if (const RecordType *RT = T->getAsStructureType()) {
    const RecordDecl *RD = RT->getDecl();
    for (RecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
         I != E; ++I) {
      QualType FieldT = I->getType();
      if (FieldT->isBlockPointerType() || FieldT->isFunctionPointerType())
        return true;
    }
  }

  return false;
}

      bool Find(const TypedValueRegion *R) {
        QualType T = R->getValueType();
        if (const RecordType *RT = T->getAsStructureType()) {
          const RecordDecl *RD = RT->getDecl()->getDefinition();
          assert(RD && "Referred record has no definition");
          for (RecordDecl::field_iterator I =
               RD->field_begin(), E = RD->field_end(); I!=E; ++I) {
            const FieldRegion *FR = MrMgr.getFieldRegion(&*I, R);
            FieldChain.push_back(&*I);
            T = I->getType();
            if (T->getAsStructureType()) {
              if (Find(FR))
                return true;
            }
            else {
              const SVal &V = StoreMgr.getBinding(store, loc::MemRegionVal(FR));
              if (V.isUndef())
                return true;
            }
            FieldChain.pop_back();
          }
        }

        return false;
      }

llvm::MDNode *
CodeGenTBAA::getTBAAStructTypeInfo(QualType QTy) {
  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
  assert(isTBAAPathStruct(QTy));

  if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
    return N;

  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
    const RecordDecl *RD = TTy->getDecl()->getDefinition();

    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
    SmallVector <std::pair<uint64_t, llvm::MDNode*>, 4> Fields;
    unsigned idx = 0;
    const FieldDecl *LastFD = 0;
    bool IsMsStruct = RD->isMsStruct(Context);
    for (RecordDecl::field_iterator i = RD->field_begin(),
         e = RD->field_end(); i != e; ++i, ++idx) {
      if (IsMsStruct) {
        // Zero-length bitfields following non-bitfield members are ignored.
        if (Context.ZeroBitfieldFollowsNonBitfield(*i, LastFD)) {
          --idx;
          continue;
        }
        LastFD = *i;
      }

      QualType FieldQTy = i->getType();
      llvm::MDNode *FieldNode;
      if (isTBAAPathStruct(FieldQTy))
        FieldNode = getTBAAStructTypeInfo(FieldQTy);
      else
        FieldNode = getTBAAInfo(FieldQTy);
      if (!FieldNode)
        return StructTypeMetadataCache[Ty] = NULL;
      Fields.push_back(std::make_pair(
          Layout.getFieldOffset(idx) / Context.getCharWidth(), FieldNode));
    }

    // 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(Ty, 0), Out);
    Out.flush();
    // Create the struct type node with a vector of pairs (offset, type).
    return StructTypeMetadataCache[Ty] =
      MDHelper.createTBAAStructTypeNode(OutName, Fields);
  }

  return StructMetadataCache[Ty] = NULL;
}

bool
CodeGenTBAA::CollectFields(uint64_t BaseOffset,
                           QualType QTy,
                           SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
                             Fields,
                           bool MayAlias) {
  /* Things not handled yet include: C++ base classes, bitfields, */

  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
    const RecordDecl *RD = TTy->getDecl()->getDefinition();
    if (RD->hasFlexibleArrayMember())
      return false;

    // TODO: Handle C++ base classes.
    if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
      if (Decl->bases_begin() != Decl->bases_end())
        return false;

    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);

    unsigned idx = 0;
    const FieldDecl *LastFD = 0;
    bool IsMsStruct = RD->isMsStruct(Context);
    for (RecordDecl::field_iterator i = RD->field_begin(),
         e = RD->field_end(); i != e; ++i, ++idx) {
      if (IsMsStruct) {
        // Zero-length bitfields following non-bitfield members are ignored.
        if (Context.ZeroBitfieldFollowsNonBitfield(*i, LastFD)) {
          --idx;
          continue;
        }
        LastFD = *i;
      }
      uint64_t Offset = BaseOffset +
                        Layout.getFieldOffset(idx) / Context.getCharWidth();
      QualType FieldQTy = i->getType();
      if (!CollectFields(Offset, FieldQTy, Fields,
                         MayAlias || TypeHasMayAlias(FieldQTy)))
        return false;
    }
    return true;
  }

  /* Otherwise, treat whatever it is as a field. */
  uint64_t Offset = BaseOffset;
  uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
  llvm::MDNode *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy);
  llvm::MDNode *TBAATag = CodeGenOpts.StructPathTBAA ?
                          getTBAAScalarTagInfo(TBAAInfo) : TBAAInfo;
  Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
  return true;
}

/// GetNumNonZeroBytesInInit - Get an approximate count of the number of
/// non-zero bytes that will be stored when outputting the initializer for the
/// specified initializer expression.
static CharUnits GetNumNonZeroBytesInInit(const Expr *E, CodeGenFunction &CGF) {
  E = E->IgnoreParens();

  // 0 and 0.0 won't require any non-zero stores!
  if (isSimpleZero(E, CGF)) return CharUnits::Zero();

  // If this is an initlist expr, sum up the size of sizes of the (present)
  // elements.  If this is something weird, assume the whole thing is non-zero.
  const InitListExpr *ILE = dyn_cast<InitListExpr>(E);
  if (ILE == 0 || !CGF.getTypes().isZeroInitializable(ILE->getType()))
    return CGF.getContext().getTypeSizeInChars(E->getType());
  
  // InitListExprs for structs have to be handled carefully.  If there are
  // reference members, we need to consider the size of the reference, not the
  // referencee.  InitListExprs for unions and arrays can't have references.
  if (const RecordType *RT = E->getType()->getAs<RecordType>()) {
    if (!RT->isUnionType()) {
      RecordDecl *SD = E->getType()->getAs<RecordType>()->getDecl();
      CharUnits NumNonZeroBytes = CharUnits::Zero();
      
      unsigned ILEElement = 0;
      for (RecordDecl::field_iterator Field = SD->field_begin(),
           FieldEnd = SD->field_end(); Field != FieldEnd; ++Field) {
        // We're done once we hit the flexible array member or run out of
        // InitListExpr elements.
        if (Field->getType()->isIncompleteArrayType() ||
            ILEElement == ILE->getNumInits())
          break;
        if (Field->isUnnamedBitfield())
          continue;

        const Expr *E = ILE->getInit(ILEElement++);
        
        // Reference values are always non-null and have the width of a pointer.
        if (Field->getType()->isReferenceType())
          NumNonZeroBytes += CGF.getContext().toCharUnitsFromBits(
              CGF.getContext().getTargetInfo().getPointerWidth(0));
        else
          NumNonZeroBytes += GetNumNonZeroBytesInInit(E, CGF);
      }
      
      return NumNonZeroBytes;
    }
  }
  
  
  CharUnits NumNonZeroBytes = CharUnits::Zero();
  for (unsigned i = 0, e = ILE->getNumInits(); i != e; ++i)
    NumNonZeroBytes += GetNumNonZeroBytesInInit(ILE->getInit(i), CGF);
  return NumNonZeroBytes;
}

llvm::MDNode *
CodeGenTBAA::getTBAAStructTypeInfo(QualType QTy) {
  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
  assert(isTBAAPathStruct(QTy));

  if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
    return N;

  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
    const RecordDecl *RD = TTy->getDecl()->getDefinition();

    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
    SmallVector <std::pair<uint64_t, llvm::MDNode*>, 4> Fields;
    // To reduce the size of MDNode for a given struct type, we only output
    // once for all the fields with the same scalar types.
    // Offsets for scalar fields in the type DAG are not used.
    llvm::SmallSet <llvm::MDNode*, 4> ScalarFieldTypes;
    unsigned idx = 0;
    for (RecordDecl::field_iterator i = RD->field_begin(),
         e = RD->field_end(); i != e; ++i, ++idx) {
      QualType FieldQTy = i->getType();
      llvm::MDNode *FieldNode;
      if (isTBAAPathStruct(FieldQTy))
        FieldNode = getTBAAStructTypeInfo(FieldQTy);
      else {
        FieldNode = getTBAAInfo(FieldQTy);
        // Ignore this field if the type already exists.
        if (ScalarFieldTypes.count(FieldNode))
          continue;
        ScalarFieldTypes.insert(FieldNode);
       }
      if (!FieldNode)
        return StructTypeMetadataCache[Ty] = NULL;
      Fields.push_back(std::make_pair(
          Layout.getFieldOffset(idx) / Context.getCharWidth(), FieldNode));
    }

    // 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(Ty, 0), Out);
    Out.flush();
    // Create the struct type node with a vector of pairs (offset, type).
    return StructTypeMetadataCache[Ty] =
      MDHelper.createTBAAStructTypeNode(OutName, Fields);
  }

  return StructMetadataCache[Ty] = NULL;
}

void CGRecordLowering::accumulateFields() {
  for (RecordDecl::field_iterator Field = D->field_begin(),
                                  FieldEnd = D->field_end();
    Field != FieldEnd;)
    if (Field->isBitField()) {
      RecordDecl::field_iterator Start = Field;
      // Iterate to gather the list of bitfields.
      for (++Field; Field != FieldEnd && Field->isBitField(); ++Field);
      accumulateBitFields(Start, Field);
    } else {
      Members.push_back(MemberInfo(
          bitsToCharUnits(getFieldBitOffset(*Field)), MemberInfo::Field,
          getStorageType(*Field), *Field));
      ++Field;
    }
}

llvm::MDNode *
CodeGenTBAA::getTBAAStructTypeInfo(QualType QTy) {
  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
  assert(isTBAAPathStruct(QTy));

  if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
    return N;

  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
    const RecordDecl *RD = TTy->getDecl()->getDefinition();

    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
    SmallVector <std::pair<llvm::MDNode*, uint64_t>, 4> Fields;
    unsigned idx = 0;
    for (RecordDecl::field_iterator i = RD->field_begin(),
         e = RD->field_end(); i != e; ++i, ++idx) {
      QualType FieldQTy = i->getType();
      llvm::MDNode *FieldNode;
      if (isTBAAPathStruct(FieldQTy))
        FieldNode = getTBAAStructTypeInfo(FieldQTy);
      else
        FieldNode = getTBAAInfo(FieldQTy);
      if (!FieldNode)
        return StructTypeMetadataCache[Ty] = NULL;
      Fields.push_back(std::make_pair(
          FieldNode, Layout.getFieldOffset(idx) / Context.getCharWidth()));
    }

    // TODO: This is using the RTTI name. Is there a better way to get
    // a unique string for a type?
    SmallString<256> OutName;
    if (Features.CPlusPlus) {
      // Don't use mangleCXXRTTIName for C code.
      llvm::raw_svector_ostream Out(OutName);
      MContext.mangleCXXRTTIName(QualType(Ty, 0), Out);
      Out.flush();
    } else {
      OutName = RD->getName();
    }
    // Create the struct type node with a vector of pairs (offset, type).
    return StructTypeMetadataCache[Ty] =
      MDHelper.createTBAAStructTypeNode(OutName, Fields);
  }

  return StructMetadataCache[Ty] = NULL;
}

  //--------------------------------------------------------- 
  void VisitInitListExpr(InitListExpr *RHS) 
  {
    unsigned elementNo = 0;
    for (RecordDecl::field_iterator i = RD->field_begin(), 
         e = RD->field_end(); i != e; ++i)
    {
      // how to handle?
      if (i->isUnnamedBitfield())
        continue;
    
      compoundStmts.push_back(Assign_(
        MemberPoint_(Paren_(Clone_(LHS)), *i), 
        elementNo < RHS->getNumInits() ?        
          Clone_ (RHS->getInit(elementNo)) : 
          Int_(0)));

      elementNo++;
    }
  }

bool
CodeGenTBAA::CollectFields(uint64_t BaseOffset,
                           QualType QTy,
                           SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
                             Fields,
                           bool MayAlias) {
  /* Things not handled yet include: C++ base classes, bitfields, */

  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
    const RecordDecl *RD = TTy->getDecl()->getDefinition();
    if (RD->hasFlexibleArrayMember())
      return false;

    // TODO: Handle C++ base classes.
    if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
      if (Decl->bases_begin() != Decl->bases_end())
        return false;

    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);

    unsigned idx = 0;
    for (RecordDecl::field_iterator i = RD->field_begin(),
         e = RD->field_end(); i != e; ++i, ++idx) {
      uint64_t Offset = BaseOffset +
                        Layout.getFieldOffset(idx) / Context.getCharWidth();
      QualType FieldQTy = i->getType();
      if (!CollectFields(Offset, FieldQTy, Fields,
                         MayAlias || TypeHasMayAlias(FieldQTy)))
        return false;
    }
    return true;
  }

  /* Otherwise, treat whatever it is as a field. */
  uint64_t Offset = BaseOffset;
  uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
  llvm::MDNode *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy);
  llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size));
  Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
  return true;
}

    bool GetFields( RecordDecl * rd, Obj * entries) {
     
        //check the fields of this struct, if any one of them is not understandable, then this struct becomes 'opaque'
        //that is, we insert the type, and link it to its llvm type, so it can be used in terra code
        //but none of its fields are exposed (since we don't understand the layout)
        bool opaque = false;
        for(RecordDecl::field_iterator it = rd->field_begin(), end = rd->field_end(); it != end; ++it) {
            if(it->isBitField() || it->isAnonymousStructOrUnion() || !it->getDeclName()) {
                opaque = true;
                continue;
            }
            DeclarationName declname = it->getDeclName();
            std::string declstr = declname.getAsString();
            QualType FT = it->getType();
            Obj fobj;
            if(!GetType(FT,&fobj)) {
                opaque = true;
                continue;
            }
            lua_newtable(L);
            fobj.push();
            lua_setfield(L,-2,"type");
            lua_pushstring(L,declstr.c_str());
            lua_setfield(L,-2,"field");
            entries->addentry();
        }
        return !opaque;

    }

/// isSafeToConvert - Return true if it is safe to convert the specified record
/// decl to IR and lay it out, false if doing so would cause us to get into a
/// recursive compilation mess.
static bool 
isSafeToConvert(const RecordDecl *RD, CodeGenTypes &CGT,
                llvm::SmallPtrSet<const RecordDecl*, 16> &AlreadyChecked) {
  // If we have already checked this type (maybe the same type is used by-value
  // multiple times in multiple structure fields, don't check again.
  if (!AlreadyChecked.insert(RD)) return true;
  
  const Type *Key = CGT.getContext().getTagDeclType(RD).getTypePtr();
  
  // If this type is already laid out, converting it is a noop.
  if (CGT.isRecordLayoutComplete(Key)) return true;
  
  // If this type is currently being laid out, we can't recursively compile it.
  if (CGT.isRecordBeingLaidOut(Key))
    return false;
  
  // If this type would require laying out bases that are currently being laid
  // out, don't do it.  This includes virtual base classes which get laid out
  // when a class is translated, even though they aren't embedded by-value into
  // the class.
  if (const CXXRecordDecl *CRD = dyn_cast<CXXRecordDecl>(RD)) {
    for (CXXRecordDecl::base_class_const_iterator I = CRD->bases_begin(),
         E = CRD->bases_end(); I != E; ++I)
      if (!isSafeToConvert(I->getType()->getAs<RecordType>()->getDecl(),
                           CGT, AlreadyChecked))
        return false;
  }
  
  // If this type would require laying out members that are currently being laid
  // out, don't do it.
  for (RecordDecl::field_iterator I = RD->field_begin(),
       E = RD->field_end(); I != E; ++I)
    if (!isSafeToConvert(I->getType(), CGT, AlreadyChecked))
      return false;
  
  // If there are no problems, lets do it.
  return true;
}

void CGRecordLayoutBuilder::LayoutUnion(const RecordDecl *D) {
  assert(D->isUnion() && "Can't call LayoutUnion on a non-union record!");

  const ASTRecordLayout &layout = Types.getContext().getASTRecordLayout(D);

  llvm::Type *unionType = 0;
  CharUnits unionSize = CharUnits::Zero();
  CharUnits unionAlign = CharUnits::Zero();

  bool hasOnlyZeroSizedBitFields = true;
  bool checkedFirstFieldZeroInit = false;

  unsigned fieldNo = 0;
  for (RecordDecl::field_iterator field = D->field_begin(),
       fieldEnd = D->field_end(); field != fieldEnd; ++field, ++fieldNo) {
    assert(layout.getFieldOffset(fieldNo) == 0 &&
          "Union field offset did not start at the beginning of record!");
    llvm::Type *fieldType = LayoutUnionField(*field, layout);

    if (!fieldType)
      continue;

    if (field->getDeclName() && !checkedFirstFieldZeroInit) {
      CheckZeroInitializable(field->getType());
      checkedFirstFieldZeroInit = true;
    }

    hasOnlyZeroSizedBitFields = false;

    CharUnits fieldAlign = CharUnits::fromQuantity(
                          Types.getDataLayout().getABITypeAlignment(fieldType));
    CharUnits fieldSize = CharUnits::fromQuantity(
                             Types.getDataLayout().getTypeAllocSize(fieldType));

    if (fieldAlign < unionAlign)
      continue;

    if (fieldAlign > unionAlign || fieldSize > unionSize) {
      unionType = fieldType;
      unionAlign = fieldAlign;
      unionSize = fieldSize;
    }
  }

  // Now add our field.
  if (unionType) {
    AppendField(CharUnits::Zero(), unionType);

    if (getTypeAlignment(unionType) > layout.getAlignment()) {
      // We need a packed struct.
      Packed = true;
      unionAlign = CharUnits::One();
    }
  }
  if (unionAlign.isZero()) {
    (void)hasOnlyZeroSizedBitFields;
    assert(hasOnlyZeroSizedBitFields &&
           "0-align record did not have all zero-sized bit-fields!");
    unionAlign = CharUnits::One();
  }

  // Append tail padding.
  CharUnits recordSize = layout.getSize();
  if (recordSize > unionSize)
    AppendPadding(recordSize, unionAlign);
}

void
CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
                                      RecordDecl::field_iterator FieldEnd) {
  // Run stores the first element of the current run of bitfields.  FieldEnd is
  // used as a special value to note that we don't have a current run.  A
  // bitfield run is a contiguous collection of bitfields that can be stored in
  // the same storage block.  Zero-sized bitfields and bitfields that would
  // cross an alignment boundary break a run and start a new one.
  RecordDecl::field_iterator Run = FieldEnd;
  // Tail is the offset of the first bit off the end of the current run.  It's
  // used to determine if the ASTRecordLayout is treating these two bitfields as
  // contiguous.  StartBitOffset is offset of the beginning of the Run.
  uint64_t StartBitOffset, Tail = 0;
  if (isDiscreteBitFieldABI()) {
    for (; Field != FieldEnd; ++Field) {
      uint64_t BitOffset = getFieldBitOffset(*Field);
      // Zero-width bitfields end runs.
      if (Field->isZeroLengthBitField(Context)) {
        Run = FieldEnd;
        continue;
      }
      llvm::Type *Type = Types.ConvertTypeForMem(Field->getType());
      // If we don't have a run yet, or don't live within the previous run's
      // allocated storage then we allocate some storage and start a new run.
      if (Run == FieldEnd || BitOffset >= Tail) {
        Run = Field;
        StartBitOffset = BitOffset;
        Tail = StartBitOffset + DataLayout.getTypeAllocSizeInBits(Type);
        // Add the storage member to the record.  This must be added to the
        // record before the bitfield members so that it gets laid out before
        // the bitfields it contains get laid out.
        Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type));
      }
      // Bitfields get the offset of their storage but come afterward and remain
      // there after a stable sort.
      Members.push_back(MemberInfo(bitsToCharUnits(StartBitOffset),
                                   MemberInfo::Field, nullptr, *Field));
    }
    return;
  }

  // Check if OffsetInRecord is better as a single field run. When OffsetInRecord
  // has legal integer width, and its bitfield offset is naturally aligned, it
  // is better to make the bitfield a separate storage component so as it can be
  // accessed directly with lower cost.
  auto IsBetterAsSingleFieldRun = [&](uint64_t OffsetInRecord,
                                      uint64_t StartBitOffset) {
    if (!Types.getCodeGenOpts().FineGrainedBitfieldAccesses)
      return false;
    if (!DataLayout.isLegalInteger(OffsetInRecord))
      return false;
    // Make sure StartBitOffset is natually aligned if it is treated as an
    // IType integer.
     if (StartBitOffset %
            Context.toBits(getAlignment(getIntNType(OffsetInRecord))) !=
        0)
      return false;
    return true;
  };

  // The start field is better as a single field run.
  bool StartFieldAsSingleRun = false;
  for (;;) {
    // Check to see if we need to start a new run.
    if (Run == FieldEnd) {
      // If we're out of fields, return.
      if (Field == FieldEnd)
        break;
      // Any non-zero-length bitfield can start a new run.
      if (!Field->isZeroLengthBitField(Context)) {
        Run = Field;
        StartBitOffset = getFieldBitOffset(*Field);
        Tail = StartBitOffset + Field->getBitWidthValue(Context);
        StartFieldAsSingleRun = IsBetterAsSingleFieldRun(Tail - StartBitOffset,
                                                         StartBitOffset); 
      }
      ++Field;
      continue;
    }

    // If the start field of a new run is better as a single run, or
    // if current field (or consecutive fields) is better as a single run, or
    // if current field has zero width bitfield and either
    // UseZeroLengthBitfieldAlignment or UseBitFieldTypeAlignment is set to
    // true, or
    // if the offset of current field is inconsistent with the offset of
    // previous field plus its offset,
    // skip the block below and go ahead to emit the storage.
    // Otherwise, try to add bitfields to the run.
    if (!StartFieldAsSingleRun && Field != FieldEnd &&
        !IsBetterAsSingleFieldRun(Tail - StartBitOffset, StartBitOffset) &&
        (!Field->isZeroLengthBitField(Context) ||
         (!Context.getTargetInfo().useZeroLengthBitfieldAlignment() &&
          !Context.getTargetInfo().useBitFieldTypeAlignment())) &&
        Tail == getFieldBitOffset(*Field)) {
      Tail += Field->getBitWidthValue(Context);
      ++Field;
      continue;
    }

//.........这里部分代码省略.........

void CGRecordLayoutBuilder::LayoutUnion(const RecordDecl *D) {
  assert(D->isUnion() && "Can't call LayoutUnion on a non-union record!");

  const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D);

  const llvm::Type *Ty = 0;
  uint64_t Size = 0;
  unsigned Align = 0;

  bool HasOnlyZeroSizedBitFields = true;
  
  unsigned FieldNo = 0;
  for (RecordDecl::field_iterator Field = D->field_begin(),
       FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
    assert(Layout.getFieldOffset(FieldNo) == 0 &&
          "Union field offset did not start at the beginning of record!");

    if (Field->isBitField()) {
      uint64_t FieldSize =
        Field->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue();

      // Ignore zero sized bit fields.
      if (FieldSize == 0)
        continue;

      // Add the bit field info.
      Types.addBitFieldInfo(*Field, 0, 0, FieldSize);
    } else
      Types.addFieldInfo(*Field, 0);

    HasOnlyZeroSizedBitFields = false;
    
    const llvm::Type *FieldTy =
      Types.ConvertTypeForMemRecursive(Field->getType());
    unsigned FieldAlign = Types.getTargetData().getABITypeAlignment(FieldTy);
    uint64_t FieldSize = Types.getTargetData().getTypeAllocSize(FieldTy);

    if (FieldAlign < Align)
      continue;

    if (FieldAlign > Align || FieldSize > Size) {
      Ty = FieldTy;
      Align = FieldAlign;
      Size = FieldSize;
    }
  }

  // Now add our field.
  if (Ty) {
    AppendField(0, Ty);

    if (getTypeAlignment(Ty) > Layout.getAlignment() / 8) {
      // We need a packed struct.
      Packed = true;
      Align = 1;
    }
  }
  if (!Align) {
    assert(HasOnlyZeroSizedBitFields &&
           "0-align record did not have all zero-sized bit-fields!");
    Align = 1;
  }
  
  // Append tail padding.
  if (Layout.getSize() / 8 > Size)
    AppendPadding(Layout.getSize() / 8, Align);
}