[NFC][FE] Replace TypeSize with StorageUnitSize

[Xiangling_L]

Summary

On some targets like AIX, last bitfield size is not always equal to last bitfield type size. Some bitfield like bool will have the same alignment as [unsigned]. So we'd like to use a more general term StorageUnit to replace type in this field.

This patch serves as a parent patch for us to add AIX bitfield related alignment rules in : https://reviews.llvm.org/D87029.

[jasonliu]

LGTM.

clang/lib/AST/RecordLayoutBuilder.cpp

1749–1751

nit: drive-by fix?
I think we should move this block of comments into the else block.

1768–1771

nit: same as the above driver-by fix.

clang/lib/AST/RecordLayoutBuilder.cpp

protected:
 
   unsigned IsMsStruct : 1;
 
   /// UnfilledBitsInLastUnit - If the last field laid out was a bitfield,
   /// this contains the number of bits in the last unit that can be used for
   /// an adjacent bitfield if necessary.  The unit in question is usually
   /// a byte, but larger units are used if IsMsStruct.
   unsigned char UnfilledBitsInLastUnit;
-  /// LastBitfieldTypeSize - If IsMsStruct, represents the size of the type
-  /// of the previous field if it was a bitfield.
-  unsigned char LastBitfieldTypeSize;
+
+  /// LastBitfieldStorageUnitSize - If IsMsStruct, represents the size of the
+  /// storage unit of the previous field if it was a bitfield.
+  unsigned char LastBitfieldStorageUnitSize;
 
   /// MaxFieldAlignment - The maximum allowed field alignment. This is set by
   /// #pragma pack.
   CharUnits MaxFieldAlignment;
 
   /// DataSize - The data size of the record being laid out.
   uint64_t DataSize;
 
protected:
   ItaniumRecordLayoutBuilder(const ASTContext &Context,
                              EmptySubobjectMap *EmptySubobjects)
       : Context(Context), EmptySubobjects(EmptySubobjects), Size(0),
         Alignment(CharUnits::One()), PreferredAlignment(CharUnits::One()),
         UnpackedAlignment(CharUnits::One()),
         UnadjustedAlignment(CharUnits::One()), UseExternalLayout(false),
         InferAlignment(false), Packed(false), IsUnion(false),
         IsMac68kAlign(false), IsMsStruct(false), UnfilledBitsInLastUnit(0),
-        LastBitfieldTypeSize(0), MaxFieldAlignment(CharUnits::Zero()),
+        LastBitfieldStorageUnitSize(0), MaxFieldAlignment(CharUnits::Zero()),
         DataSize(0), NonVirtualSize(CharUnits::Zero()),
         NonVirtualAlignment(CharUnits::One()),
         PreferredNVAlignment(CharUnits::One()),
         PaddedFieldSize(CharUnits::Zero()), PrimaryBase(nullptr),
         PrimaryBaseIsVirtual(false), HasOwnVFPtr(false), HasPackedField(false),
         HandledFirstNonOverlappingEmptyField(false),
         FirstNearlyEmptyVBase(nullptr) {}
 
   void Layout(const RecordDecl *D);
   void Layout(const CXXRecordDecl *D);
   void Layout(const ObjCInterfaceDecl *D);
 
   void LayoutFields(const RecordDecl *D);
   void LayoutField(const FieldDecl *D, bool InsertExtraPadding);
-  void LayoutWideBitField(uint64_t FieldSize, uint64_t TypeSize,
+  void LayoutWideBitField(uint64_t FieldSize, uint64_t StorageUnitSize,
                           bool FieldPacked, const FieldDecl *D);
   void LayoutBitField(const FieldDecl *D);
 
   TargetCXXABI getCXXABI() const {
     return Context.getTargetInfo().getCXXABI();
   }
 
   /// BaseSubobjectInfoAllocator - Allocator for BaseSubobjectInfo objects.

 static uint64_t
 roundUpSizeToCharAlignment(uint64_t Size,
                            const ASTContext &Context) {
   uint64_t CharAlignment = Context.getTargetInfo().getCharAlign();
   return llvm::alignTo(Size, CharAlignment);
 }
 
 void ItaniumRecordLayoutBuilder::LayoutWideBitField(uint64_t FieldSize,
-                                                    uint64_t TypeSize,
+                                                    uint64_t StorageUnitSize,
                                                     bool FieldPacked,
                                                     const FieldDecl *D) {
   assert(Context.getLangOpts().CPlusPlus &&
          "Can only have wide bit-fields in C++!");
 
   // Itanium C++ ABI 2.4:
   //   If sizeof(T)*8 < n, let T' be the largest integral POD type with
   //   sizeof(T')*8 <= n.
for (const QualType &QT : IntegralPODTypes) {
     Type = QT;
   }
   assert(!Type.isNull() && "Did not find a type!");
 
   CharUnits TypeAlign = Context.getTypeAlignInChars(Type);
 
   // We're not going to use any of the unfilled bits in the last byte.
   UnfilledBitsInLastUnit = 0;
-  LastBitfieldTypeSize = 0;
+  LastBitfieldStorageUnitSize = 0;
 
   uint64_t FieldOffset;
   uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
 
   if (IsUnion) {
     uint64_t RoundedFieldSize = roundUpSizeToCharAlignment(FieldSize,
                                                            Context);
     setDataSize(std::max(getDataSizeInBits(), RoundedFieldSize));
void ItaniumRecordLayoutBuilder::LayoutWideBitField(uint64_t FieldSize,
   // Remember max struct/class alignment.
   UpdateAlignment(TypeAlign);
 }
 
 void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
   uint64_t FieldSize = D->getBitWidthValue(Context);
   TypeInfo FieldInfo = Context.getTypeInfo(D->getType());
-  uint64_t TypeSize = FieldInfo.Width;
+  uint64_t StorageUnitSize = FieldInfo.Width;
   unsigned FieldAlign = FieldInfo.Align;
 
   // UnfilledBitsInLastUnit is the difference between the end of the
   // last allocated bitfield (i.e. the first bit offset available for
   // bitfields) and the end of the current data size in bits (i.e. the
   // first bit offset available for non-bitfields).  The current data
   // size in bits is always a multiple of the char size; additionally,
   // for ms_struct records it's also a multiple of the
-  // LastBitfieldTypeSize (if set).
+  // LastBitfieldStorageUnitSize (if set).
 
   // The struct-layout algorithm is dictated by the platform ABI,
   // which in principle could use almost any rules it likes.  In
   // practice, UNIXy targets tend to inherit the algorithm described
   // in the System V generic ABI.  The basic bitfield layout rule in
   // System V is to place bitfields at the next available bit offset
   // where the entire bitfield would fit in an aligned storage unit of
   // the declared type; it's okay if an earlier or later non-bitfield
void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   // In an ms_struct struct, the alignment of a fundamental type is
   // always equal to its size.  This is necessary in order to mimic
   // the i386 alignment rules on targets which might not fully align
   // all types (e.g. Darwin PPC32, where alignof(long long) == 4).
 
   // First, some simple bookkeeping to perform for ms_struct structs.
   if (IsMsStruct) {
     // The field alignment for integer types is always the size.
-    FieldAlign = TypeSize;
+    FieldAlign = StorageUnitSize;
 
     // If the previous field was not a bitfield, or was a bitfield
     // with a different storage unit size, or if this field doesn't fit into
     // the current storage unit, we're done with that storage unit.
-    if (LastBitfieldTypeSize != TypeSize ||
+    if (LastBitfieldStorageUnitSize != StorageUnitSize ||
         UnfilledBitsInLastUnit < FieldSize) {
       // Also, ignore zero-length bitfields after non-bitfields.
-      if (!LastBitfieldTypeSize && !FieldSize)
+      if (!LastBitfieldStorageUnitSize && !FieldSize)
         FieldAlign = 1;
 
       UnfilledBitsInLastUnit = 0;
-      LastBitfieldTypeSize = 0;
+      LastBitfieldStorageUnitSize = 0;
     }
   }
 
   // If the field is wider than its declared type, it follows
   // different rules in all cases.
-  if (FieldSize > TypeSize) {
-    LayoutWideBitField(FieldSize, TypeSize, FieldPacked, D);
+  if (FieldSize > StorageUnitSize) {
+    LayoutWideBitField(FieldSize, StorageUnitSize, FieldPacked, D);
     return;
   }
 
   // Compute the next available bit offset.
   uint64_t FieldOffset =
     IsUnion ? 0 : (getDataSizeInBits() - UnfilledBitsInLastUnit);
 
   // Handle targets that don't honor bitfield type alignment.
void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
 
   } else {
     // #pragma pack, with any value, suppresses the insertion of padding.
     bool AllowPadding = MaxFieldAlignment.isZero();
 
     // Compute the real offset.
     if (FieldSize == 0 ||
         (AllowPadding &&
-         (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)) {
+         (FieldOffset & (FieldAlign - 1)) + FieldSize > StorageUnitSize)) {
       FieldOffset = llvm::alignTo(FieldOffset, FieldAlign);
     } else if (ExplicitFieldAlign &&
                (MaxFieldAlignmentInBits == 0 ||
                 ExplicitFieldAlign <= MaxFieldAlignmentInBits) &&
                Context.getTargetInfo().useExplicitBitFieldAlignment()) {
       // TODO: figure it out what needs to be done on targets that don't honor
       // bit-field type alignment like ARM APCS ABI.
       FieldOffset = llvm::alignTo(FieldOffset, ExplicitFieldAlign);
     }
 
     // Repeat the computation for diagnostic purposes.
     if (FieldSize == 0 ||
         (AllowPadding &&
-         (UnpackedFieldOffset & (UnpackedFieldAlign-1)) + FieldSize > TypeSize))
+         (UnpackedFieldOffset & (UnpackedFieldAlign - 1)) + FieldSize >
+             StorageUnitSize))
       UnpackedFieldOffset =
           llvm::alignTo(UnpackedFieldOffset, UnpackedFieldAlign);
     else if (ExplicitFieldAlign &&
              (MaxFieldAlignmentInBits == 0 ||
               ExplicitFieldAlign <= MaxFieldAlignmentInBits) &&
              Context.getTargetInfo().useExplicitBitFieldAlignment())
       UnpackedFieldOffset =
           llvm::alignTo(UnpackedFieldOffset, ExplicitFieldAlign);
void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   // Update DataSize to include the last byte containing (part of) the bitfield.
 
   // For unions, this is just a max operation, as usual.
   if (IsUnion) {
     // For ms_struct, allocate the entire storage unit --- unless this
     // is a zero-width bitfield, in which case just use a size of 1.
     uint64_t RoundedFieldSize;
     if (IsMsStruct) {
-      RoundedFieldSize =
-        (FieldSize ? TypeSize : Context.getTargetInfo().getCharWidth());
+      RoundedFieldSize = (FieldSize ? StorageUnitSize
+                                    : Context.getTargetInfo().getCharWidth());
 
       // Otherwise, allocate just the number of bytes required to store
       // the bitfield.
     } else {
       RoundedFieldSize = roundUpSizeToCharAlignment(FieldSize, Context);
     }
     setDataSize(std::max(getDataSizeInBits(), RoundedFieldSize));
 
   // For non-zero-width bitfields in ms_struct structs, allocate a new
   // storage unit if necessary.
   } else if (IsMsStruct && FieldSize) {
     // We should have cleared UnfilledBitsInLastUnit in every case
     // where we changed storage units.
     if (!UnfilledBitsInLastUnit) {
-      setDataSize(FieldOffset + TypeSize);
-      UnfilledBitsInLastUnit = TypeSize;
+      setDataSize(FieldOffset + StorageUnitSize);
+      UnfilledBitsInLastUnit = StorageUnitSize;
     }
     UnfilledBitsInLastUnit -= FieldSize;
-    LastBitfieldTypeSize = TypeSize;
+    LastBitfieldStorageUnitSize = StorageUnitSize;
 
     // Otherwise, bump the data size up to include the bitfield,
     // including padding up to char alignment, and then remember how
     // bits we didn't use.
   } else {
     uint64_t NewSizeInBits = FieldOffset + FieldSize;
     uint64_t CharAlignment = Context.getTargetInfo().getCharAlign();
     setDataSize(llvm::alignTo(NewSizeInBits, CharAlignment));
     UnfilledBitsInLastUnit = getDataSizeInBits() - NewSizeInBits;
 
     // The only time we can get here for an ms_struct is if this is a
     // zero-width bitfield, which doesn't count as anything for the
     // purposes of unfilled bits.
-    LastBitfieldTypeSize = 0;
+    LastBitfieldStorageUnitSize = 0;
   }
 
   // Update the size.
   setSize(std::max(getSizeInBits(), getDataSizeInBits()));
 
   // Remember max struct/class alignment.
   UnadjustedAlignment =
       std::max(UnadjustedAlignment, Context.toCharUnitsFromBits(FieldAlign));
void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
   if (D->isBitField()) {
     LayoutBitField(D);
     return;
   }
 
   uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
   // Reset the unfilled bits.
   UnfilledBitsInLastUnit = 0;
-  LastBitfieldTypeSize = 0;
+  LastBitfieldStorageUnitSize = 0;
 
   bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
 
   bool AlignIsRequired = false;
   CharUnits FieldSize;
   CharUnits FieldAlign;
   // The amount of this class's dsize occupied by the field.
   // This is equal to FieldSize unless we're permitted to pack