[codeview] Added support for bitfield type

[aaboud]

Summary

Added support for bitfield type for record members.

[majnemer]

lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

1549–1562

Inferring the properties of the bitfield is problematic, consider:

#pragma pack(1)
struct S {
  char x;
  int y : 2;
  int z : 2;
};
S s;

You will give back:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 2
  BitOffset: 8
}
BitField (0x1002) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 2
  BitOffset: 10
}
UnknownLeaf (0x1003) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: char (0x70)
    FieldOffset: 0x0
    Name: x
  }
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x0
    Name: y
  }
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1002
    FieldOffset: 0x0
    Name: z
  }
}

I would think the correct output to be:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 2
  BitOffset: 0
}
BitField (0x1002) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 2
  BitOffset: 2
}
UnknownLeaf (0x1003) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: char (0x70)
    FieldOffset: 0x0
    Name: x
  }
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x4
    Name: y
  }
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1002
    FieldOffset: 0x4
    Name: z
  }
}

Perhaps we need to encode the storage offset for the bitfield in the metadata?

[aaboud]

Improved solution and LIT test, thanks to the example David provided.

[majnemer]

This approach still seems a little problematic, consider:

#pragma pack(1)
struct S {
  char  : 0;
  int y : 1;
};
S s;

Your code will produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 8
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x0
    Name: y
  }
}

However, I think it should produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 0
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x1
    Name: y
  }
}

I'm pretty sure that the only real way to get bitfields right is by encoding the storage offset in the DI metadata.

[aaboud]

In D21489#462178, @majnemer wrote:

This approach still seems a little problematic, consider:

#pragma pack(1)
struct S {
  char  : 0;
  int y : 1;
};
S s;

Your code will produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 8
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x0
    Name: y
  }
}

However, I think it should produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 0
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x1
    Name: y
  }
}

I'm pretty sure that the only real way to get bitfields right is by encoding the storage offset in the DI metadata.

I think my code will produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 0
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x0
    Name: y
  }
}

Which is the same as MS cl.

[majnemer]

In D21489#463372, @aaboud wrote:

In D21489#462178, @majnemer wrote:

This approach still seems a little problematic, consider:

#pragma pack(1)
struct S {
  char  : 0;
  int y : 1;
};
S s;

Your code will produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 8
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x0
    Name: y
  }
}

However, I think it should produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 0
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x1
    Name: y
  }
}

I'm pretty sure that the only real way to get bitfields right is by encoding the storage offset in the DI metadata.

I think my code will produce:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: int (0x74)
  BitSize: 1
  BitOffset: 0
}
UnknownLeaf (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x0
    Name: y
  }
}

Which is the same as MS cl.

Would you mind adding it as a test case? Also, can you please rebase your patch? I cannot seem to apply it to trunk.

[aaboud]

Add more cases to the LIT test.
Updated patch to top of trunk.

[majnemer]

Consider this input:

#pragma pack(1)
struct S {
  char    : 8;
  short   : 8;
  short x : 8;
} s;

Your patch appears to give:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: short (0x11)
  BitSize: 8
  BitOffset: 0
}
FieldList (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x2
    Name: x
  }
}

MSVC gives:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: short (0x11)
  BitSize: 8
  BitOffset: 8
}
FieldList (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x1
    Name: x
  }
}

[aaboud]

In D21489#467609, @majnemer wrote:

Consider this input:

#pragma pack(1)
struct S {
  char    : 8;
  short   : 8;
  short x : 8;
} s;

Your patch appears to give:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: short (0x11)
  BitSize: 8
  BitOffset: 0
}
FieldList (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x2
    Name: x
  }
}

MSVC gives:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: short (0x11)
  BitSize: 8
  BitOffset: 8
}
FieldList (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x1
    Name: x
  }
}

You are right, this case is not handled correctly yet.
However, this is because Clang (FE) does not provide the information, this is how LLVM IR looks like:

!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !1, line: 2, size: 24, align: 8, elements: !6, identifier: ".?AUS@@")
!6 = !{!7}
!7 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !5, file: !1, line: 5, baseType: !8, size: 8, align: 16, offset: 16)
!8 = !DIBasicType(name: "short", size: 16, align: 16, encoding: DW_ATE_signed)

and this how it should look like to fix the problem, once we make Clang emit the following the above code will work:

!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !1, line: 2, size: 24, align: 8, elements: !6, identifier: ".?AUS@@")
!6 = !{!7, !9, 11}
!7 = !DIDerivedType(tag: DW_TAG_member, scope: !5, file: !1, line: 3, baseType: !8, size: 8, align: 8, offset: 0)
!8 = !DIBasicType(name: "char", size: 8, align: 8, encoding: DW_ATE_signed)
!9 = !DIDerivedType(tag: DW_TAG_member, scope: !5, file: !1, line: 4, baseType: !10, size: 8, align: 16, offset: 8)
!10 = !DIBasicType(name: "short", size: 16, align: 16, encoding: DW_ATE_signed)
!11 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !5, file: !1, line: 5, baseType: !11, size: 8, align: 16, offset: 16)

Then all we need to do, is not to emit members with no name, but to consider the size and alignment they consume.

[majnemer]

In D21489#467653, @aaboud wrote:

In D21489#467609, @majnemer wrote:

Consider this input:

#pragma pack(1)
struct S {
  char    : 8;
  short   : 8;
  short x : 8;
} s;

Your patch appears to give:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: short (0x11)
  BitSize: 8
  BitOffset: 0
}
FieldList (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x2
    Name: x
  }
}

MSVC gives:

BitField (0x1001) {
  TypeLeafKind: LF_BITFIELD (0x1205)
  Type: short (0x11)
  BitSize: 8
  BitOffset: 8
}
FieldList (0x1002) {
  TypeLeafKind: LF_FIELDLIST (0x1203)
  DataMember {
    AccessSpecifier: Public (0x3)
    Type: 0x1001
    FieldOffset: 0x1
    Name: x
  }
}

You are right, this case is not handled correctly yet.
However, this is because Clang (FE) does not provide the information, this is how LLVM IR looks like:

!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !1, line: 2, size: 24, align: 8, elements: !6, identifier: ".?AUS@@")
!6 = !{!7}
!7 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !5, file: !1, line: 5, baseType: !8, size: 8, align: 16, offset: 16)
!8 = !DIBasicType(name: "short", size: 16, align: 16, encoding: DW_ATE_signed)

and this how it should look like to fix the problem, once we make Clang emit the following the above code will work:

!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !1, line: 2, size: 24, align: 8, elements: !6, identifier: ".?AUS@@")
!6 = !{!7, !9, 11}
!7 = !DIDerivedType(tag: DW_TAG_member, scope: !5, file: !1, line: 3, baseType: !8, size: 8, align: 8, offset: 0)
!8 = !DIBasicType(name: "char", size: 8, align: 8, encoding: DW_ATE_signed)
!9 = !DIDerivedType(tag: DW_TAG_member, scope: !5, file: !1, line: 4, baseType: !10, size: 8, align: 16, offset: 8)
!10 = !DIBasicType(name: "short", size: 16, align: 16, encoding: DW_ATE_signed)
!11 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !5, file: !1, line: 5, baseType: !11, size: 8, align: 16, offset: 16)

Then all we need to do, is not to emit members with no name, but to consider the size and alignment they consume.

I don't think this is a good idea. It would be far cheaper to encode the offset of the underlying allocation in the extraData.

[aaboud]

Added support of unnamed bitfield.

[aaboud]

I don't think this is a good idea. It would be far cheaper to encode the offset of the underlying allocation in the extraData.

Please, review the last version of the patch and the patch for clang (D21766).
I think these patches complete the support for all bitfield cases.
However, if you have a better way to implement this support, I do not mind to abandon these patches.

Thanks.

[aaboud]

Different implementation was committed at rL274200.

lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

 }
 
 void CodeViewDebug::collectMemberInfo(ClassInfo &Info,
                                       const DIDerivedType *DDTy) {
   if (!DDTy->getName().empty()) {
     Info.Members.push_back({DDTy, 0});
     return;
   }
-  // An unnamed member must represent a nested struct or union. Add all the
+  // If an unnamed member represents a nested struct or union, add all the
   // indirect fields to the current record.
-  assert((DDTy->getOffsetInBits() % 8) == 0 && "Unnamed bitfield member!");
-  unsigned Offset = DDTy->getOffsetInBits() / 8;
   const DIType *Ty = DDTy->getBaseType().resolve();
+  if (isa<DICompositeType>(Ty)) {
+    unsigned Offset = DDTy->getOffsetInBits() / 8;
     const DICompositeType *DCTy = cast<DICompositeType>(Ty);
     ClassInfo NestedInfo = collectClassInfo(DCTy);
     for (const ClassInfo::MemberInfo &IndirectField : NestedInfo.Members)
       Info.Members.push_back(
           {IndirectField.MemberTypeNode, IndirectField.BaseOffset + Offset});
   }
 
+  // At this point an unnamed member must be a bitfield member, add it to
+  // Members list for later handling.
+  Info.Members.push_back({ DDTy, 0 });
+}
+
 ClassInfo CodeViewDebug::collectClassInfo(const DICompositeType *Ty) {
   ClassInfo Info;
   // Add elements to structure type.
   DINodeArray Elements = Ty->getElements();
   for (auto *Element : Elements) {
     // We assume that the frontend provides all members in source declaration
     // order, which is what MSVC does.
     if (!Element)
TypeTable.writeUdtSourceLine(UdtSourceLineRecord(
                    TypeIndex(0x0), getFullFilepath(Ty->getFile()))),
       Ty->getLine()));
 
   addToUDTs(Ty, UnionTI);
 
   return UnionTI;
 }
 
+/// If this type is derived from a base type then return base type size.
+static uint64_t getBaseTypeSize(const DIDerivedType *Ty) {
+  unsigned Tag = Ty->getTag();
+
+  if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
+      Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
+      Tag != dwarf::DW_TAG_restrict_type)
+    return Ty->getSizeInBits();
+
+  DIType *BaseType = Ty->getBaseType().resolve();
+
+  // If this type is not derived from any type or the type is a declaration then
+  // take conservative approach.
+  if (!BaseType || BaseType->isForwardDecl())
+    return Ty->getSizeInBits();
+
+  // If this is a derived type, go ahead and get the base type, unless it's a
+  // reference then it's just the size of the field. Pointer types have no need
+  // of this since they're a different type of qualification on the type.
+  if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
+      BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
+    return Ty->getSizeInBits();
+
+  if (DIDerivedType *DT = dyn_cast<DIDerivedType>(BaseType))
+    return getBaseTypeSize(DT);
+
+  return BaseType->getSizeInBits();
+}
+
 std::tuple<TypeIndex, TypeIndex, unsigned>
 CodeViewDebug::lowerRecordFieldList(const DICompositeType *Ty) {
   // Manually count members. MSVC appears to count everything that generates a
   // field list record. Each individual overload in a method overload group
   // contributes to this count, even though the overload group is a single field
   // list record.
   unsigned MemberCount = 0;
   ClassInfo Info = collectClassInfo(Ty);
if (I->getFlags() & DINode::FlagVirtual) {
              "bases must be on byte boundaries");
       Fields.writeBaseClass(BaseClassRecord(
           translateAccessFlags(Ty->getTag(), I->getFlags()),
           getTypeIndex(I->getBaseType()), I->getOffsetInBits() / 8));
     }
   }
 
   // Create members.
+  uint64_t PrevAlignment = 0;
+  uint64_t PrevFieldSize = 0;
+  uint64_t BaseOffset = 0;
   for (ClassInfo::MemberInfo &MemberInfo : Info.Members) {
     const DIDerivedType *Member = MemberInfo.MemberTypeNode;
     TypeIndex MemberBaseType = getTypeIndex(Member->getBaseType());
 
     if (Member->isStaticMember()) {
       Fields.writeStaticDataMember(StaticDataMemberRecord(
           translateAccessFlags(Ty->getTag(), Member->getFlags()),
           MemberBaseType, Member->getName()));
       MemberCount++;
       continue;
     }
 
+    // Do not emit unnamed members.
+    // We need them only to calculate the offsets of other members.
+    bool ToEmitMember = !Member->getName().empty();
+
+    uint64_t Alignment = Member->getAlignInBits();
+    uint64_t Offset = Member->getOffsetInBits();
+    uint64_t Size = Member->getSizeInBits();
+    uint64_t FieldSize = getBaseTypeSize(Member);
     uint64_t OffsetInBytes = MemberInfo.BaseOffset;
 
-    // FIXME: Handle bitfield type memeber.
-    OffsetInBytes += Member->getOffsetInBits() / 8;
+
+    if (Size != FieldSize) {
+      // If alignment was changed, increase BaseOffset with PrevFieldSize.
+      if (PrevAlignment != Alignment)
+        BaseOffset += PrevFieldSize;
+
+      Offset -= BaseOffset;
+
+      // If Offset equals or exceeds Alignment, adjust BaseOffset and Offset.
+      if (Offset >= Alignment) {
+        uint64_t RealOffset = Offset % Alignment;
+        BaseOffset += (Offset - RealOffset);
+        Offset = RealOffset;
+      }
+
+      if (ToEmitMember)
+        MemberBaseType = TypeTable.writeBitField(
+            BitFieldRecord(MemberBaseType, (uint8_t)Size, (uint8_t)Offset));
+      OffsetInBytes += BaseOffset / 8;
+    } else {
+      // This is not a bitfield.
+      OffsetInBytes += Offset / 8;
+      BaseOffset += PrevFieldSize;
+    }
+
+    // Update previous field size and alignment.
+    PrevAlignment = Alignment;
+    PrevFieldSize = FieldSize;
+
+    if (!ToEmitMember)
+      continue;
 
     Fields.writeDataMember(
         DataMemberRecord(translateAccessFlags(Ty->getTag(), Member->getFlags()),
                          MemberBaseType, OffsetInBytes, Member->getName()));
     MemberCount++;
   }
 
   // Create methods

test/DebugInfo/COFF/types-bitfield.ll

+; RUN: llc < %s -filetype=obj | llvm-readobj - -codeview | FileCheck %s
+
+; C++ source to regenerate:
+; $ cat t.cpp
+; #pragma pack(1)
+; struct S1 {
+;   char x1[2];
+;   char x2;
+;   int y : 23;
+;   int z : 23;
+;   int w : 2;
+;   struct { char c; short s; } v;
+;   short u : 3;
+; } s1;
+;
+; #pragma pack(1)
+; struct S2 {
+;   char  : 0;
+;   int y : 1;
+; } s2;
+;
+; #pragma pack(1)
+; struct S3 {
+;   char : 8;
+;   short : 8;
+;   short x : 8;
+; } s3;
+; $ clang t.cpp -S -emit-llvm -g -gcodeview -o t.ll
+
+; CHECK: CodeViewTypes [
+; CHECK:   Section: .debug$T (5)
+; CHECK:   Magic: 0x4
+; CHECK:   Struct (0x1000) {
+; CHECK:     TypeLeafKind: LF_STRUCTURE (0x1505)
+; CHECK:     MemberCount: 0
+; CHECK:     Properties [ (0x280)
+; CHECK:       ForwardReference (0x80)
+; CHECK:       HasUniqueName (0x200)
+; CHECK:     ]
+; CHECK:     FieldList: 0x0
+; CHECK:     DerivedFrom: 0x0
+; CHECK:     VShape: 0x0
+; CHECK:     SizeOf: 0
+; CHECK:     Name: S
+; CHECK:     LinkageName: .?AUS1@@
+; CHECK:   }
+; CHECK:   Array (0x1001) {
+; CHECK:     TypeLeafKind: LF_ARRAY (0x1503)
+; CHECK:     ElementType: char (0x70)
+; CHECK:     IndexType: unsigned long (0x22)
+; CHECK:     SizeOf: 2
+; CHECK:     Name: 
+; CHECK:   }
+; CHECK:   BitField (0x1002) {
+; CHECK:     TypeLeafKind: LF_BITFIELD (0x1205)
+; CHECK:     Type: int (0x74)
+; CHECK:     BitSize: 23
+; CHECK:     BitOffset: 0
+; CHECK:   }
+; CHECK:   BitField (0x1003) {
+; CHECK:     TypeLeafKind: LF_BITFIELD (0x1205)
+; CHECK:     Type: int (0x74)
+; CHECK:     BitSize: 2
+; CHECK:     BitOffset: 23
+; CHECK:   }
+; CHECK:   Struct (0x1004) {
+; CHECK:     TypeLeafKind: LF_STRUCTURE (0x1505)
+; CHECK:     MemberCount: 0
+; CHECK:     Properties [ (0x280)
+; CHECK:       ForwardReference (0x80)
+; CHECK:       HasUniqueName (0x200)
+; CHECK:     ]
+; CHECK:     FieldList: 0x0
+; CHECK:     DerivedFrom: 0x0
+; CHECK:     VShape: 0x0
+; CHECK:     SizeOf: 0
+; CHECK:     Name: 
+; CHECK:     LinkageName: .?AU<unnamed-type-v>@S1@@
+; CHECK:   }
+; CHECK:   BitField (0x1005) {
+; CHECK:     TypeLeafKind: LF_BITFIELD (0x1205)
+; CHECK:     Type: short (0x11)
+; CHECK:     BitSize: 3
+; CHECK:     BitOffset: 0
+; CHECK:   }
+; CHECK:   FieldList (0x1006) {
+; CHECK:     TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: 0x1001
+; CHECK:       FieldOffset: 0x0
+; CHECK:       Name: x1
+; CHECK:     }
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: char (0x70)
+; CHECK:       FieldOffset: 0x2
+; CHECK:       Name: x2
+; CHECK:     }
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: 0x1002
+; CHECK:       FieldOffset: 0x3
+; CHECK:       Name: y
+; CHECK:     }
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: 0x1002
+; CHECK:       FieldOffset: 0x7
+; CHECK:       Name: z
+; CHECK:     }
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: 0x1003
+; CHECK:       FieldOffset: 0x7
+; CHECK:       Name: w
+; CHECK:     }
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: S1:: (0x1004)
+; CHECK:       FieldOffset: 0xB
+; CHECK:       Name: v
+; CHECK:     }
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: 0x1005
+; CHECK:       FieldOffset: 0xE
+; CHECK:       Name: u
+; CHECK:     }
+; CHECK:   }
+; CHECK:   Struct (0x1007) {
+; CHECK:     TypeLeafKind: LF_STRUCTURE (0x1505)
+; CHECK:     MemberCount: 7
+; CHECK:     Properties [ (0x200)
+; CHECK:       HasUniqueName (0x200)
+; CHECK:     ]
+; CHECK:     FieldList: <field list> (0x1006)
+; CHECK:     DerivedFrom: 0x0
+; CHECK:     VShape: 0x0
+; CHECK:     SizeOf: 16
+; CHECK:     Name: S
+; CHECK:     LinkageName: .?AUS1@@
+; CHECK:   }
+;
+; CHECK:   FieldList (0x100A) {
+; CHECK:     TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: char (0x70)
+; CHECK:       FieldOffset: 0x0
+; CHECK:       Name: c
+; CHECK:     }
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: short (0x11)
+; CHECK:       FieldOffset: 0x1
+; CHECK:       Name: s
+; CHECK:     }
+; CHECK:   }
+; CHECK:   Struct (0x100B) {
+; CHECK:     TypeLeafKind: LF_STRUCTURE (0x1505)
+; CHECK:     MemberCount: 2
+; CHECK:     Properties [ (0x200)
+; CHECK:       HasUniqueName (0x200)
+; CHECK:     ]
+; CHECK:     FieldList: <field list> (0x100A)
+; CHECK:     DerivedFrom: 0x0
+; CHECK:     VShape: 0x0
+; CHECK:     SizeOf: 3
+; CHECK:     Name: S1::
+; CHECK:     LinkageName: .?AU<unnamed-type-v>@S1@@
+; CHECK:   }
+;
+; CHECK:   BitField (0x100E) {
+; CHECK:     TypeLeafKind: LF_BITFIELD (0x1205)
+; CHECK:     Type: int (0x74)
+; CHECK:     BitSize: 1
+; CHECK:     BitOffset: 0
+; CHECK:   }
+; CHECK:   FieldList (0x100F) {
+; CHECK:     TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: 0x100E
+; CHECK:       FieldOffset: 0x0
+; CHECK:       Name: y
+; CHECK:     }
+; CHECK:   }
+; CHECK:   Struct (0x1010) {
+; CHECK:     TypeLeafKind: LF_STRUCTURE (0x1505)
+; CHECK:     MemberCount: 1
+; CHECK:     Properties [ (0x200)
+; CHECK:       HasUniqueName (0x200)
+; CHECK:     ]
+; CHECK:     FieldList: <field list> (0x100F)
+; CHECK:     DerivedFrom: 0x0
+; CHECK:     VShape: 0x0
+; CHECK:     SizeOf: 4
+; CHECK:     Name: S2
+; CHECK:     LinkageName: .?AUS2@@
+; CHECK:   }
+;
+; CHECK:   BitField (0x1013) {
+; CHECK:     TypeLeafKind: LF_BITFIELD (0x1205)
+; CHECK:     Type: short (0x11)
+; CHECK:     BitSize: 8
+; CHECK:     BitOffset: 8
+; CHECK:   }
+; CHECK:   FieldList (0x1014) {
+; CHECK:     TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK:     DataMember {
+; CHECK:       AccessSpecifier: Public (0x3)
+; CHECK:       Type: 0x1013
+; CHECK:       FieldOffset: 0x1
+; CHECK:       Name: x
+; CHECK:     }
+; CHECK:   }
+; CHECK:   Struct (0x1015) {
+; CHECK:     TypeLeafKind: LF_STRUCTURE (0x1505)
+; CHECK:     MemberCount: 1
+; CHECK:     Properties [ (0x200)
+; CHECK:       HasUniqueName (0x200)
+; CHECK:     ]
+; CHECK:     FieldList: <field list> (0x1014)
+; CHECK:     DerivedFrom: 0x0
+; CHECK:     VShape: 0x0
+; CHECK:     SizeOf: 3
+; CHECK:     Name: S3
+; CHECK:     LinkageName: .?AUS3@@
+; CHECK:   }
+; CHECK: ]
+
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.31101"
+
+%struct.S1 = type <{ [2 x i8], i8, i32, i32, %struct.anon, i16 }>
+%struct.anon = type <{ i8, i16 }>
+%struct.S2 = type { i32 }
+%struct.S3 = type <{ i8, i16 }>
+
+@"\01?s1@@3US1@@A" = global %struct.S1 zeroinitializer, align 1
+@"\01?s2@@3US2@@A" = global %struct.S2 zeroinitializer, align 1
+@"\01?s3@@3US3@@A" = global %struct.S3 zeroinitializer, align 1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!34, !35}
+!llvm.ident = !{!36}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.9.0 (trunk 273874)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3)
+!1 = !DIFile(filename: "t.cpp", directory: "/")
+!2 = !{}
+!3 = !{!4, !24, !28}
+!4 = distinct !DIGlobalVariable(name: "s1", linkageName: "\01?s1@@3US1@@A", scope: !0, file: !1, line: 10, type: !5, isLocal: false, isDefinition: true, variable: %struct.S1* @"\01?s1@@3US1@@A")
+!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S1", file: !1, line: 2, size: 128, align: 8, elements: !6, identifier: ".?AUS1@@")
+!6 = !{!7, !12, !13, !15, !16, !17, !23}
+!7 = !DIDerivedType(tag: DW_TAG_member, name: "x1", scope: !5, file: !1, line: 3, baseType: !8, size: 16, align: 8)
+!8 = !DICompositeType(tag: DW_TAG_array_type, baseType: !9, size: 16, align: 8, elements: !10)
+!9 = !DIBasicType(name: "char", size: 8, align: 8, encoding: DW_ATE_signed_char)
+!10 = !{!11}
+!11 = !DISubrange(count: 2)
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "x2", scope: !5, file: !1, line: 4, baseType: !9, size: 8, align: 8, offset: 16)
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !5, file: !1, line: 5, baseType: !14, size: 23, align: 32, offset: 24)
+!14 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!15 = !DIDerivedType(tag: DW_TAG_member, name: "z", scope: !5, file: !1, line: 6, baseType: !14, size: 23, align: 32, offset: 56)
+!16 = !DIDerivedType(tag: DW_TAG_member, name: "w", scope: !5, file: !1, line: 7, baseType: !14, size: 2, align: 32, offset: 79)
+!17 = !DIDerivedType(tag: DW_TAG_member, name: "v", scope: !5, file: !1, line: 8, baseType: !18, size: 24, align: 8, offset: 88)
+!18 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !5, file: !1, line: 8, size: 24, align: 8, elements: !19, identifier: ".?AU<unnamed-type-v>@S1@@")
+!19 = !{!20, !21}
+!20 = !DIDerivedType(tag: DW_TAG_member, name: "c", scope: !18, file: !1, line: 8, baseType: !9, size: 8, align: 8)
+!21 = !DIDerivedType(tag: DW_TAG_member, name: "s", scope: !18, file: !1, line: 8, baseType: !22, size: 16, align: 16, offset: 8)
+!22 = !DIBasicType(name: "short", size: 16, align: 16, encoding: DW_ATE_signed)
+!23 = !DIDerivedType(tag: DW_TAG_member, name: "u", scope: !5, file: !1, line: 9, baseType: !22, size: 3, align: 16, offset: 112)
+!24 = distinct !DIGlobalVariable(name: "s2", linkageName: "\01?s2@@3US2@@A", scope: !0, file: !1, line: 16, type: !25, isLocal: false, isDefinition: true, variable: %struct.S2* @"\01?s2@@3US2@@A")
+!25 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S2", file: !1, line: 13, size: 32, align: 8, elements: !26, identifier: ".?AUS2@@")
+!26 = !{!27}
+!27 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !25, file: !1, line: 15, baseType: !14, size: 1, align: 32)
+!28 = distinct !DIGlobalVariable(name: "s3", linkageName: "\01?s3@@3US3@@A", scope: !0, file: !1, line: 23, type: !29, isLocal: false, isDefinition: true, variable: %struct.S3* @"\01?s3@@3US3@@A")
+!29 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S3", file: !1, line: 19, size: 24, align: 8, elements: !30, identifier: ".?AUS3@@")
+!30 = !{!31, !32, !33}
+!31 = !DIDerivedType(tag: DW_TAG_member, scope: !29, file: !1, line: 20, baseType: !9, size: 8, align: 8)
+!32 = !DIDerivedType(tag: DW_TAG_member, scope: !29, file: !1, line: 21, baseType: !22, size: 8, align: 16, offset: 8)
+!33 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !29, file: !1, line: 22, baseType: !22, size: 8, align: 16, offset: 16)
+!34 = !{i32 2, !"CodeView", i32 1}
+!35 = !{i32 2, !"Debug Info Version", i32 3}
+!36 = !{!"clang version 3.9.0 (trunk 273874)"}