[CodeView] Improve debbuging of virtual base class member variables

[bwyma]

Summary

Right now the virtual base pointer offset for virtual bases is not implemented and hard-coded to zero in CodeViewDebug.cpp. This patch passes the offset from clang to CodeView where it can be emitted. The crux of the patch looks like this:

-      // FIXME: Emit VBPtrOffset when the frontend provides it.
-      unsigned VBPtrOffset = 0;
+      unsigned VBPtrOffset = I->getVBPtrOffset();

The rest of the source changes support embedding this single field in the IR and reading/writing it to bitcode.

Inheritance is currently encoded in the IR as a DIDerivedType which is currently reused for several other purposes. Four tests which have bitcode files containing a DIDerivedType needed to have the bitcode file updated. Three of these bitcode files were not marked in subversion as a binary file, so I also set the mime-type accordingly.

The diglobalvariable.ll file did not appear to get updated to match changes made to diglobalvariable.bc when DIGlobalVariableExpression was added. Since I had to regenerate the bitcode file anyways I also updated the ".ll" file accordingly.

[rnk]

llvm/include/llvm/IR/DebugInfoMetadata.h

794–795

vbptroffset is pretty esoteric. It seems really unfortunate to have to widen the very popular DIDerivedType constructor to take this obscure parameter. Pointer and reference types are some of the most common kinds of DIDerivedType nodes, so taking an address space is less objectionable, even though it is specialized towards one kind of derived type node.

I'd recommend encoding this information in the extraData field, similar to how we encode bit offsets for bitfields, or making a new DIInheritanceType node. @aprantl, @dblaikie WDYT?

[aprantl]

llvm/include/llvm/IR/DebugInfoMetadata.h

794

please drop the \brief.

794–795

Seems reasonable; avoiding making DIDerivedType larger for all languages and platforms would be a good thing.

[bwyma]

Document a comment I received via email from David to keep everything in one place:

Bitcode files shouldn't generally need updating - because bitcode should be backwards compatible (& indeed usually the only reason bitcode files are checked in is to test and ensure that backwards compatibility guarantee is met)

[bwyma]

llvm/include/llvm/IR/DebugInfoMetadata.h

794–795

Although I believe DIInheritedType is a better solution, changing DW_TAG_inheritance from DIDerivedType to DIInheritedType is a substantial change which I would recommend making independently from this fix. Furthermore, your valid argument regarding the esoteric nature of the field will be just as valid for DIInheritedType as it is for DIDerivedType, so I think in either case the field should be moved to extraData. As a result, for the purposes of this patch I propose moving this field to the extraData field of DIDerivedType. Is this sufficient?

[rnk]

llvm/include/llvm/IR/DebugInfoMetadata.h

794–795

Yep, sounds good to me.

[bwyma]

llvm/include/llvm/IR/DebugInfoMetadata.h

794

please drop the \brief.

I have no personal attachment to this tag and I would be happy to remove it, but it matches the surrounding code and seems to be permitted by the coding standard. Can you explain why it should be removed?

[aprantl]

llvm/include/llvm/IR/DebugInfoMetadata.h

794

Sure! A few years ago we started enabling autobrief mode in LLVM's Doxygen configuration, which makes the use of \brief in the source code redundant. It's a distraction when reading the source code, so we shouldn't add it in new code and probably also remove it from existing code.

[rnk]

llvm/include/llvm/IR/DebugInfoMetadata.h

794

Given that I've seen you raise this comment a few times, I think it's probably worth doing a large pass to remove \brief across LLVM. Otherwise people will continue to copy it in an effort to fit in with existing code, and then we'll spend time on it during review.

[dexonsmith]

llvm/include/llvm/IR/DebugInfoMetadata.h

794–795

SGTM too.

[aprantl]

llvm/include/llvm/IR/DebugInfoMetadata.h

794

I think it's probably worth doing a large pass to remove \brief across LLVM.

Done! -> https://reviews.llvm.org/D46290

[bwyma]

The virtual base pointer offset is now encoded in the extraData field of DIDerivedType.

[rnk]

lgtm, thanks!

[bwyma]

In the test inheritance.ll I updated the 'variables' attribute to 'retainedNodes' to reflect the changes recently committed in rL331841.

[bwyma]

Changes committed in rL332296.

llvm/include/llvm/IR/DIBuilder.h

public:
     /// Create debugging information entry for a 'friend'.
     DIDerivedType *createFriend(DIType *Ty, DIType *FriendTy);
 
     /// Create debugging information entry to establish
     /// inheritance relationship between two types.
     /// \param Ty           Original type.
     /// \param BaseTy       Base type. Ty is inherits from base.
     /// \param BaseOffset   Base offset.
+    /// \param VBPtrOffset  Virtual base pointer offset.
     /// \param Flags        Flags to describe inheritance attribute,
     ///                     e.g. private
     DIDerivedType *createInheritance(DIType *Ty, DIType *BaseTy,
-                                     uint64_t BaseOffset,
+                                     uint64_t BaseOffset, uint32_t VBPtrOffset,
                                      DINode::DIFlags Flags);
 
     /// Create debugging information entry for a member.
     /// \param Scope        Member scope.
     /// \param Name         Member name.
     /// \param File         File where this member is defined.
     /// \param LineNo       Line number.
     /// \param SizeInBits   Member size.

llvm/include/llvm/IR/DebugInfoMetadata.h

 /// This includes qualified types, pointers, references, friends, typedefs, and
 /// class members.
 ///
 /// TODO: Split out members (inheritance, fields, methods, etc.).
 class DIDerivedType : public DIType {
   friend class LLVMContextImpl;
   friend class MDNode;
 
   /// The DWARF address space of the memory pointed to or referenced by a
   /// pointer or reference type respectively.
   Optional<unsigned> DWARFAddressSpace;
 
   DIDerivedType(LLVMContext &C, StorageType Storage, unsigned Tag,
                 unsigned Line, uint64_t SizeInBits, uint32_t AlignInBits,
                 uint64_t OffsetInBits, Optional<unsigned> DWARFAddressSpace,
                 DIFlags Flags, ArrayRef<Metadata *> Ops)
       : DIType(C, DIDerivedTypeKind, Storage, Tag, Line, SizeInBits,
                AlignInBits, OffsetInBits, Flags, Ops),
public:
 
   /// \returns The DWARF address space of the memory pointed to or referenced by
   /// a pointer or reference type respectively.
   Optional<unsigned> getDWARFAddressSpace() const { return DWARFAddressSpace; }
 
   /// Get extra data associated with this derived type.
   ///
   /// Class type for pointer-to-members, objective-c property node for ivars,
-  /// or global constant wrapper for static members.
+  /// global constant wrapper for static members, or virtual base pointer offset
+  /// for inheritance.
   ///
   /// TODO: Separate out types that need this extra operand: pointer-to-member
   /// types and member fields (static members and ivars).
   Metadata *getExtraData() const { return getRawExtraData(); }
   Metadata *getRawExtraData() const { return getOperand(4); }
 
   /// Get casted version of extra data.
   /// @{
   DITypeRef getClassType() const {
     assert(getTag() == dwarf::DW_TAG_ptr_to_member_type);
     return DITypeRef(getExtraData());
   }
 
   DIObjCProperty *getObjCProperty() const {
     return dyn_cast_or_null<DIObjCProperty>(getExtraData());
   }
 
+  uint32_t getVBPtrOffset() const {
+    assert(getTag() == dwarf::DW_TAG_inheritance);
+    if (auto *CM = cast_or_null<ConstantAsMetadata>(getExtraData()))
+      if (auto *CI = dyn_cast_or_null<ConstantInt>(CM->getValue()))
+        return static_cast<uint32_t>(CI->getZExtValue());
+    return 0;
+  }
+
   Constant *getStorageOffsetInBits() const {
     assert(getTag() == dwarf::DW_TAG_member && isBitField());
     if (auto *C = cast_or_null<ConstantAsMetadata>(getExtraData()))
       return C->getValue();
     return nullptr;
   }
 
   Constant *getConstant() const {

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

CodeViewDebug::lowerRecordFieldList(const DICompositeType *Ty) {
   ClassInfo Info = collectClassInfo(Ty);
   ContinuationRecordBuilder ContinuationBuilder;
   ContinuationBuilder.begin(ContinuationRecordKind::FieldList);
 
   // Create base classes.
   for (const DIDerivedType *I : Info.Inheritance) {
     if (I->getFlags() & DINode::FlagVirtual) {
       // Virtual base.
-      // FIXME: Emit VBPtrOffset when the frontend provides it.
-      unsigned VBPtrOffset = 0;
+      unsigned VBPtrOffset = I->getVBPtrOffset();
       // FIXME: Despite the accessor name, the offset is really in bytes.
       unsigned VBTableIndex = I->getOffsetInBits() / 4;
       auto RecordKind = (I->getFlags() & DINode::FlagIndirectVirtualBase) == DINode::FlagIndirectVirtualBase
                             ? TypeRecordKind::IndirectVirtualBaseClass
                             : TypeRecordKind::VirtualBaseClass;
       VirtualBaseClassRecord VBCR(
           RecordKind, translateAccessFlags(Ty->getTag(), I->getFlags()),
           getTypeIndex(I->getBaseType()), getVBPTypeIndex(), VBPtrOffset,

llvm/lib/IR/DIBuilder.cpp

DIDerivedType *DIBuilder::createFriend(DIType *Ty, DIType *FriendTy) {
   assert(Ty && "Invalid type!");
   assert(FriendTy && "Invalid friend type!");
   return DIDerivedType::get(VMContext, dwarf::DW_TAG_friend, "", nullptr, 0, Ty,
                             FriendTy, 0, 0, 0, None, DINode::FlagZero);
 }
 
 DIDerivedType *DIBuilder::createInheritance(DIType *Ty, DIType *BaseTy,
                                             uint64_t BaseOffset,
+                                            uint32_t VBPtrOffset,
                                             DINode::DIFlags Flags) {
   assert(Ty && "Unable to create inheritance");
+  Metadata *ExtraData = ConstantAsMetadata::get(
+      ConstantInt::get(IntegerType::get(VMContext, 32), VBPtrOffset));
   return DIDerivedType::get(VMContext, dwarf::DW_TAG_inheritance, "", nullptr,
-                            0, Ty, BaseTy, 0, 0, BaseOffset, None, Flags);
+                            0, Ty, BaseTy, 0, 0, BaseOffset, None,
+                            Flags, ExtraData);
 }
 
 DIDerivedType *DIBuilder::createMemberType(DIScope *Scope, StringRef Name,
                                            DIFile *File, unsigned LineNumber,
                                            uint64_t SizeInBits,
                                            uint32_t AlignInBits,
                                            uint64_t OffsetInBits,
                                            DINode::DIFlags Flags, DIType *Ty) {

llvm/test/DebugInfo/COFF/inheritance.ll

 ; RUN: llc < %s -filetype=obj -o - | llvm-readobj - -codeview | FileCheck %s
 
 ; C++ source to regenerate:
 ; $ cat t.cpp
 ; struct A { int a; };
-; struct B : virtual A { int b; };
-; struct C : virtual A { int c; };
+; struct B : virtual A { int b; virtual int get() { return b; } };
+; struct C : virtual A { int c; virtual int get() { return c; } };
 ; struct D : B, C {
 ;   virtual void f(); // make vbptr not offset zero
 ;   int d;
 ; };
 ; D d;
 ; $ clang -fno-rtti -g -gcodeview t.cpp -emit-llvm -S -o t.ll -O1
 
-; D's field list comes first.
+; struct B's field list comes first.
 ; CHECK:        FieldList ({{.*}}) {
 ; CHECK-NEXT:     TypeLeafKind: LF_FIELDLIST (0x1203)
-; CHECK-NEXT:     BaseClass {
-; CHECK-NEXT:       TypeLeafKind: LF_BCLASS (0x1400)
-; CHECK-NEXT:       AccessSpecifier: Public (0x3)
-; CHECK-NEXT:       BaseType: B ({{.*}})
-; CHECK-NEXT:       BaseOffset: 0x8
-; CHECK-NEXT:     }
-; CHECK-NEXT:     BaseClass {
-; CHECK-NEXT:       TypeLeafKind: LF_BCLASS (0x1400)
-; CHECK-NEXT:       AccessSpecifier: Public (0x3)
-; CHECK-NEXT:       BaseType: C ({{.*}})
-; CHECK-NEXT:       BaseOffset: 0x18
-; CHECK-NEXT:     }
-; CHECK-NEXT:     IndirectVirtualBaseClass {
-; CHECK-NEXT:       TypeLeafKind: LF_IVBCLASS (0x1402)
+; CHECK-NEXT:     VirtualBaseClass {
+; CHECK-NEXT:       TypeLeafKind: LF_VBCLASS (0x1401)
 ; CHECK-NEXT:       AccessSpecifier: Public (0x3)
 ; CHECK-NEXT:       BaseType: A ({{.*}})
 ; CHECK-NEXT:       VBPtrType: const int* ({{.*}})
-; CHECK-NEXT:       VBPtrOffset: 0x0
+; CHECK-NEXT:       VBPtrOffset: 0x8
 ; CHECK-NEXT:       VBTableIndex: 0x1
 ; CHECK-NEXT:     }
 ; CHECK:        }
 
-; Then B's field list.
-; CHECK:        FieldList ({{.*}}) {
-; CHECK-NEXT:     TypeLeafKind: LF_FIELDLIST (0x1203)
-; CHECK-NEXT:     VirtualBaseClass {
-; CHECK-NEXT:       TypeLeafKind: LF_VBCLASS (0x1401)
-; CHECK-NEXT:       AccessSpecifier: Public (0x3)
-; CHECK-NEXT:       BaseType: A ({{.*}})
-; CHECK-NEXT:       VBPtrType: const int* ({{.*}})
-; CHECK-NEXT:       VBPtrOffset: 0x0
-; CHECK-NEXT:       VBTableIndex: 0x1
-; CHECK-NEXT:     }
-; CHECK:        }
+; struct A's field list comes next.
+; CHECK:       FieldList ({{.*}})
+; CHECK-NEXT:    TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK:       }
+
+; struct C's field list comes next.
+; CHECK:       FieldList ({{.*}})
+; CHECK-NEXT:    TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK-NEXT:    VirtualBaseClass {
+; CHECK-NEXT:      TypeLeafKind: LF_VBCLASS (0x1401)
+; CHECK-NEXT:      AccessSpecifier: Public (0x3)
+; CHECK-NEXT:      BaseType: A ({{.*}})
+; CHECK-NEXT:      VBPtrType: const int* ({{.*}})
+; CHECK-NEXT:      VBPtrOffset: 0x8
+; CHECK-NEXT:      VBTableIndex: 0x1
+; CHECK-NEXT:    }
+; CHECK:       }
 
-; Then C's field list.
-; CHECK:        FieldList ({{.*}}) {
-; CHECK-NEXT:     TypeLeafKind: LF_FIELDLIST (0x1203)
-; CHECK-NEXT:     VirtualBaseClass {
-; CHECK-NEXT:       TypeLeafKind: LF_VBCLASS (0x1401)
-; CHECK-NEXT:       AccessSpecifier: Public (0x3)
-; CHECK-NEXT:       BaseType: A ({{.*}})
-; CHECK-NEXT:       VBPtrType: const int* ({{.*}})
-; CHECK-NEXT:       VBPtrOffset: 0x0
-; CHECK-NEXT:       VBTableIndex: 0x1
-; CHECK-NEXT:     }
-; CHECK:        }
+; struct D's field list is last.
+; CHECK:       FieldList ({{.*}}) {
+; CHECK-NEXT:    TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK-NEXT:    BaseClass {
+; CHECK-NEXT:      TypeLeafKind: LF_BCLASS (0x1400)
+; CHECK-NEXT:      AccessSpecifier: Public (0x3)
+; CHECK-NEXT:      BaseType: B ({{.*}})
+; CHECK-NEXT:      BaseOffset: 0x0
+; CHECK-NEXT:    }
+; CHECK-NEXT:    BaseClass {
+; CHECK-NEXT:      TypeLeafKind: LF_BCLASS (0x1400)
+; CHECK-NEXT:      AccessSpecifier: Public (0x3)
+; CHECK-NEXT:      BaseType: C ({{.*}})
+; CHECK-NEXT:      BaseOffset: 0x18
+; CHECK-NEXT:    }
+; CHECK-NEXT:    IndirectVirtualBaseClass {
+; CHECK-NEXT:      TypeLeafKind: LF_IVBCLASS (0x1402)
+; CHECK-NEXT:      AccessSpecifier: Public (0x3)
+; CHECK-NEXT:      BaseType: A ({{.*}})
+; CHECK-NEXT:      VBPtrType: const int* ({{.*}})
+; CHECK-NEXT:      VBPtrOffset: 0x8
+; CHECK-NEXT:      VBTableIndex: 0x1
+; CHECK-NEXT:    }
+; CHECK:       }
 
 ; ModuleID = 't.cpp'
 source_filename = "t.cpp"
 target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
-target triple = "x86_64-pc-windows-msvc19.0.23918"
+target triple = "x86_64-pc-windows-msvc19.12.25835"
 
-%struct.D = type { i32 (...)**, %struct.B.base, %struct.C.base, i32, [4 x i8], %struct.A }
-%struct.B.base = type { i32*, i32 }
-%struct.C.base = type { i32*, i32 }
+%struct.D = type { %struct.B.base, %struct.C.base, i32, [4 x i8], %struct.A }
+%struct.B.base = type { i32 (...)**, i32*, i32 }
+%struct.C.base = type { i32 (...)**, i32*, i32 }
 %struct.A = type { i32 }
+%struct.B = type { i32 (...)**, i32*, i32, [4 x i8], %struct.A }
+%struct.C = type { i32 (...)**, i32*, i32, [4 x i8], %struct.A }
 
-$"\01??_8D@@7BB@@@" = comdat any
+$"?get@B@@UEAAHXZ" = comdat any
 
-$"\01??_8D@@7BC@@@" = comdat any
+$"?get@C@@UEAAHXZ" = comdat any
 
-$"\01??_7D@@6B@" = comdat any
+$"??_8D@@7BB@@@" = comdat any
 
-@"\01?d@@3UD@@A" = local_unnamed_addr global %struct.D { i32 (...)** bitcast ([1 x i8*]* @"\01??_7D@@6B@" to i32 (...)**), %struct.B.base { i32* getelementptr inbounds ([2 x i32], [2 x i32]* @"\01??_8D@@7BB@@@", i32 0, i32 0), i32 0 }, %struct.C.base { i32* getelementptr inbounds ([2 x i32], [2 x i32]* @"\01??_8D@@7BC@@@", i32 0, i32 0), i32 0 }, i32 0, [4 x i8] zeroinitializer, %struct.A zeroinitializer }, align 8, !dbg !0
-@"\01??_8D@@7BB@@@" = linkonce_odr unnamed_addr constant [2 x i32] [i32 0, i32 40], comdat
-@"\01??_8D@@7BC@@@" = linkonce_odr unnamed_addr constant [2 x i32] [i32 0, i32 24], comdat
-@"\01??_7D@@6B@" = linkonce_odr unnamed_addr constant [1 x i8*] [i8* bitcast (void (%struct.D*)* @"\01?f@D@@UEAAXXZ" to i8*)], comdat
[e-mail]_ctors = appending global [0 x { i32, void ()*, i8* }] zeroinitializer
+$"??_8D@@7BC@@@" = comdat any
 
-declare void @"\01?f@D@@UEAAXXZ"(%struct.D*) unnamed_addr #0
+$"??_7D@@6BB@@@" = comdat any
 
-attributes #0 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+$"??_7D@@6BC@@@" = comdat any
+
+@"?d@@3UD@@A" = dso_local local_unnamed_addr global %struct.D { %struct.B.base { i32 (...)** bitcast ({ [2 x i8*] }* @"??_7D@@6BB@@@" to i32 (...)**), i32* getelementptr inbounds ([2 x i32], [2 x i32]* @"??_8D@@7BB@@@", i32 0, i32 0), i32 0 }, %struct.C.base { i32 (...)** bitcast ({ [1 x i8*] }* @"??_7D@@6BC@@@" to i32 (...)**), i32* getelementptr inbounds ([2 x i32], [2 x i32]* @"??_8D@@7BC@@@", i32 0, i32 0), i32 0 }, i32 0, [4 x i8] zeroinitializer, %struct.A zeroinitializer }, align 8, !dbg !0
+@"??_8D@@7BB@@@" = linkonce_odr unnamed_addr constant [2 x i32] [i32 -8, i32 48], comdat
+@"??_8D@@7BC@@@" = linkonce_odr unnamed_addr constant [2 x i32] [i32 -8, i32 24], comdat
+@"??_7D@@6BB@@@" = linkonce_odr unnamed_addr constant { [2 x i8*] } { [2 x i8*] [i8* bitcast (i32 (%struct.B*)* @"?get@B@@UEAAHXZ" to i8*), i8* bitcast (void (%struct.D*)* @"?f@D@@UEAAXXZ" to i8*)] }, comdat
+@"??_7D@@6BC@@@" = linkonce_odr unnamed_addr constant { [1 x i8*] } { [1 x i8*] [i8* bitcast (i32 (%struct.C*)* @"?get@C@@UEAAHXZ" to i8*)] }, comdat
[e-mail]_ctors = appending global [0 x { i32, void ()*, i8* }] zeroinitializer
+
+; Function Attrs: nounwind uwtable
+define linkonce_odr dso_local i32 @"?get@B@@UEAAHXZ"(%struct.B* %this) unnamed_addr #0 comdat align 2 !dbg !46 {
+entry:
+  call void @llvm.dbg.value(metadata %struct.B* %this, metadata !48, metadata !DIExpression()), !dbg !50
+  %b = getelementptr inbounds %struct.B, %struct.B* %this, i64 0, i32 2, !dbg !51
+  %0 = load i32, i32* %b, align 8, !dbg !51, !tbaa !52
+  ret i32 %0, !dbg !51
+}
+
+declare dso_local void @"?f@D@@UEAAXXZ"(%struct.D*) unnamed_addr #1
+
+; Function Attrs: nounwind uwtable
+define linkonce_odr dso_local i32 @"?get@C@@UEAAHXZ"(%struct.C* %this) unnamed_addr #0 comdat align 2 !dbg !57 {
+entry:
+  call void @llvm.dbg.value(metadata %struct.C* %this, metadata !59, metadata !DIExpression()), !dbg !61
+  %c = getelementptr inbounds %struct.C, %struct.C* %this, i64 0, i32 2, !dbg !62
+  %0 = load i32, i32* %c, align 8, !dbg !62, !tbaa !63
+  ret i32 %0, !dbg !62
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+attributes #0 = { nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind readnone speculatable }
 
 !llvm.dbg.cu = !{!2}
-!llvm.module.flags = !{!32, !33, !34}
-!llvm.ident = !{!35}
+!llvm.module.flags = !{!41, !42, !43, !44}
+!llvm.ident = !{!45}
 
-!0 = distinct !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
-!1 = !DIGlobalVariable(name: "d", linkageName: "\01?d@@3UD@@A", scope: !2, file: !6, line: 8, type: !7, isLocal: false, isDefinition: true)
-!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 4.0.0 (http://llvm.org/git/clang.git 95626d54d6db7e13087089396a80ebaccc4ffe7c) (http://llvm.org/git/llvm.git 374b6e2fa0b230d13c0fb9ee7af69b2146bfad8a)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
-!3 = !DIFile(filename: "t.cpp", directory: "D:\5Csrc\5Cllvm\5Cbuild")
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "d", linkageName: "?d@@3UD@@A", scope: !2, file: !3, line: 8, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 7.0.0 (trunk)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "t.cpp", directory: "C:\5CPath\5CTo\5CDirectory", checksumkind: CSK_MD5, checksum: "7477d4db6bf8a461a719bcaab9c6d65e")
 !4 = !{}
 !5 = !{!0}
-!6 = !DIFile(filename: "t.cpp", directory: "C:\5Cbuild\5Cllvm\5Cbuild")
-!7 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "D", file: !6, line: 4, size: 448, elements: !8, vtableHolder: !7, identifier: ".?AUD@@")
-!8 = !{!9, !18, !23, !24, !25, !27, !28}
-!9 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !7, baseType: !10, offset: 64)
-!10 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "B", file: !6, line: 2, size: 192, elements: !11, vtableHolder: !10, identifier: ".?AUB@@")
-!11 = !{!12, !17}
-!12 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !10, baseType: !13, offset: 4, flags: DIFlagVirtual)
-!13 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "A", file: !6, line: 1, size: 32, elements: !14, identifier: ".?AUA@@")
-!14 = !{!15}
-!15 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !13, file: !6, line: 1, baseType: !16, size: 32)
-!16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
-!17 = !DIDerivedType(tag: DW_TAG_member, name: "b", scope: !10, file: !6, line: 2, baseType: !16, size: 32, offset: 64)
-!18 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !7, baseType: !19, offset: 192)
-!19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "C", file: !6, line: 3, size: 192, elements: !20, vtableHolder: !19, identifier: ".?AUC@@")
-!20 = !{!21, !22}
-!21 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !19, baseType: !13, offset: 4, flags: DIFlagVirtual)
-!22 = !DIDerivedType(tag: DW_TAG_member, name: "c", scope: !19, file: !6, line: 3, baseType: !16, size: 32, offset: 64)
-!23 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !7, baseType: !13, offset: 4, flags: DIFlagIndirectVirtualBase)
-!24 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "__vtbl_ptr_type", baseType: null, size: 64)
-!25 = !DIDerivedType(tag: DW_TAG_member, name: "_vptr$D", scope: !6, file: !6, baseType: !26, size: 64, flags: DIFlagArtificial)
-!26 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !24, size: 64)
-!27 = !DIDerivedType(tag: DW_TAG_member, name: "d", scope: !7, file: !6, line: 6, baseType: !16, size: 32, offset: 320)
-!28 = !DISubprogram(name: "f", linkageName: "\01?f@D@@UEAAXXZ", scope: !7, file: !6, line: 5, type: !29, isLocal: false, isDefinition: false, scopeLine: 5, containingType: !7, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, flags: DIFlagPrototyped | DIFlagIntroducedVirtual, isOptimized: true)
-!29 = !DISubroutineType(types: !30)
-!30 = !{null, !31}
-!31 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !7, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
-!32 = !{i32 2, !"CodeView", i32 1}
-!33 = !{i32 2, !"Debug Info Version", i32 3}
-!34 = !{i32 1, !"PIC Level", i32 2}
-!35 = !{!"clang version 4.0.0 (http://llvm.org/git/clang.git 95626d54d6db7e13087089396a80ebaccc4ffe7c) (http://llvm.org/git/llvm.git 374b6e2fa0b230d13c0fb9ee7af69b2146bfad8a)"}
-
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "D", file: !3, line: 4, size: 512, flags: DIFlagTypePassByReference, elements: !7, vtableHolder: !9, identifier: ".?AUD@@")
+!7 = !{!8, !24, !34, !35, !36, !37}
+!8 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !6, baseType: !9, extraData: i32 0)
+!9 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "B", file: !3, line: 2, size: 256, flags: DIFlagTypePassByReference, elements: !10, vtableHolder: !9, identifier: ".?AUB@@")
+!10 = !{!11, !16, !17, !19, !20}
+!11 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !9, baseType: !12, offset: 4, flags: DIFlagVirtual, extraData: i32 8)
+!12 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "A", file: !3, line: 1, size: 32, flags: DIFlagTypePassByValue, elements: !13, identifier: ".?AUA@@")
+!13 = !{!14}
+!14 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !12, file: !3, line: 1, baseType: !15, size: 32)
+!15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!16 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "__vtbl_ptr_type", baseType: null, size: 64)
+!17 = !DIDerivedType(tag: DW_TAG_member, name: "_vptr$B", scope: !3, file: !3, baseType: !18, size: 64, flags: DIFlagArtificial)
+!18 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 64)
+!19 = !DIDerivedType(tag: DW_TAG_member, name: "b", scope: !9, file: !3, line: 2, baseType: !15, size: 32, offset: 128)
+!20 = !DISubprogram(name: "get", linkageName: "?get@B@@UEAAHXZ", scope: !9, file: !3, line: 2, type: !21, isLocal: false, isDefinition: false, scopeLine: 2, containingType: !9, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, flags: DIFlagPrototyped | DIFlagIntroducedVirtual, isOptimized: true)
+!21 = !DISubroutineType(types: !22)
+!22 = !{!15, !23}
+!23 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!24 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !6, baseType: !25, offset: 192, extraData: i32 0)
+!25 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "C", file: !3, line: 3, size: 256, flags: DIFlagTypePassByReference, elements: !26, vtableHolder: !25, identifier: ".?AUC@@")
+!26 = !{!27, !16, !28, !29, !30}
+!27 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !25, baseType: !12, offset: 4, flags: DIFlagVirtual, extraData: i32 8)
+!28 = !DIDerivedType(tag: DW_TAG_member, name: "_vptr$C", scope: !3, file: !3, baseType: !18, size: 64, flags: DIFlagArtificial)
+!29 = !DIDerivedType(tag: DW_TAG_member, name: "c", scope: !25, file: !3, line: 3, baseType: !15, size: 32, offset: 128)
+!30 = !DISubprogram(name: "get", linkageName: "?get@C@@UEAAHXZ", scope: !25, file: !3, line: 3, type: !31, isLocal: false, isDefinition: false, scopeLine: 3, containingType: !25, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, flags: DIFlagPrototyped | DIFlagIntroducedVirtual, isOptimized: true)
+!31 = !DISubroutineType(types: !32)
+!32 = !{!15, !33}
+!33 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !25, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!34 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !6, baseType: !12, offset: 4, flags: DIFlagIndirectVirtualBase, extraData: i32 8)
+!35 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "__vtbl_ptr_type", baseType: null, size: 128)
+!36 = !DIDerivedType(tag: DW_TAG_member, name: "d", scope: !6, file: !3, line: 6, baseType: !15, size: 32, offset: 384)
+!37 = !DISubprogram(name: "f", linkageName: "?f@D@@UEAAXXZ", scope: !6, file: !3, line: 5, type: !38, isLocal: false, isDefinition: false, scopeLine: 5, containingType: !6, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 1, flags: DIFlagPrototyped | DIFlagIntroducedVirtual, isOptimized: true)
+!38 = !DISubroutineType(types: !39)
+!39 = !{null, !40}
+!40 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !6, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!41 = !{i32 2, !"CodeView", i32 1}
+!42 = !{i32 2, !"Debug Info Version", i32 3}
+!43 = !{i32 1, !"wchar_size", i32 2}
+!44 = !{i32 7, !"PIC Level", i32 2}
+!45 = !{!"clang version 7.0.0 (trunk)"}
+!46 = distinct !DISubprogram(name: "get", linkageName: "?get@B@@UEAAHXZ", scope: !9, file: !3, line: 2, type: !21, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !2, declaration: !20, retainedNodes: !47)
+!47 = !{!48}
+!48 = !DILocalVariable(name: "this", arg: 1, scope: !46, type: !49, flags: DIFlagArtificial | DIFlagObjectPointer)
+!49 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
+!50 = !DILocation(line: 0, scope: !46)
+!51 = !DILocation(line: 2, scope: !46)
+!52 = !{!53, !54, i64 16}
+!53 = !{!"?AUB@@", !54, i64 16}
+!54 = !{!"int", !55, i64 0}
+!55 = !{!"omnipotent char", !56, i64 0}
+!56 = !{!"Simple C++ TBAA"}
+!57 = distinct !DISubprogram(name: "get", linkageName: "?get@C@@UEAAHXZ", scope: !25, file: !3, line: 3, type: !31, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !2, declaration: !30, retainedNodes: !58)
+!58 = !{!59}
+!59 = !DILocalVariable(name: "this", arg: 1, scope: !57, type: !60, flags: DIFlagArtificial | DIFlagObjectPointer)
+!60 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !25, size: 64)
+!61 = !DILocation(line: 0, scope: !57)
+!62 = !DILocation(line: 3, scope: !57)
+!63 = !{!64, !54, i64 16}
+!64 = !{!"?AUC@@", !54, i64 16}

llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp

void CGDebugInfo::CollectCXXBasesAux(
   for (const auto &BI : Bases) {
     const auto *Base =
         cast<CXXRecordDecl>(BI.getType()->getAs<RecordType>()->getDecl());
     if (!SeenTypes.insert(Base).second)
       continue;
     auto *BaseTy = getOrCreateType(BI.getType(), Unit);
     llvm::DINode::DIFlags BFlags = StartingFlags;
     uint64_t BaseOffset;
+    uint32_t VBPtrOffset = 0;
 
     if (BI.isVirtual()) {
       if (CGM.getTarget().getCXXABI().isItaniumFamily()) {
         // virtual base offset offset is -ve. The code generator emits dwarf
         // expression where it expects +ve number.
         BaseOffset = 0 - CGM.getItaniumVTableContext()
                              .getVirtualBaseOffsetOffset(RD, Base)
                              .getQuantity();
       } else {
         // In the MS ABI, store the vbtable offset, which is analogous to the
         // vbase offset offset in Itanium.
         BaseOffset =
             4 * CGM.getMicrosoftVTableContext().getVBTableIndex(RD, Base);
+        VBPtrOffset = CGM.getContext().getASTRecordLayout(RD).getVBPtrOffset()
+                         .getQuantity();
       }
       BFlags |= llvm::DINode::FlagVirtual;
     } else
       BaseOffset = CGM.getContext().toBits(RL.getBaseClassOffset(Base));
     // FIXME: Inconsistent units for BaseOffset. It is in bytes when
     // BI->isVirtual() and bits when not.
 
     BFlags |= getAccessFlag(BI.getAccessSpecifier(), RD);
     llvm::DIType *DTy =
-        DBuilder.createInheritance(RecordTy, BaseTy, BaseOffset, BFlags);
+        DBuilder.createInheritance(RecordTy, BaseTy, BaseOffset, VBPtrOffset,
+                                   BFlags);
     EltTys.push_back(DTy);
   }
 }
 
 llvm::DINodeArray
 CGDebugInfo::CollectTemplateParams(const TemplateParameterList *TPList,
                                    ArrayRef<TemplateArgument> TAList,
                                    llvm::DIFile *Unit) {
llvm::DIType *CGDebugInfo::CreateTypeDefinition(const ObjCInterfaceType *Ty,
 
   ObjCInterfaceDecl *SClass = ID->getSuperClass();
   if (SClass) {
     llvm::DIType *SClassTy =
         getOrCreateType(CGM.getContext().getObjCInterfaceType(SClass), Unit);
     if (!SClassTy)
       return nullptr;
 
-    llvm::DIType *InhTag = DBuilder.createInheritance(RealDecl, SClassTy, 0,
+    llvm::DIType *InhTag = DBuilder.createInheritance(RealDecl, SClassTy, 0, 0,
                                                       llvm::DINode::FlagZero);
     EltTys.push_back(InhTag);
   }
 
   // Create entries for all of the properties.
   auto AddProperty = [&](const ObjCPropertyDecl *PD) {
     SourceLocation Loc = PD->getLocation();
     llvm::DIFile *PUnit = getOrCreateFile(Loc);

llvm/tools/clang/test/CodeGenCXX/debug-info-access.cpp

 // RUN: %clang_cc1 -emit-llvm -debug-info-kind=limited -triple %itanium_abi_triple %s -o - | FileCheck %s
 // Test the various accessibility flags in the debug info.
 struct A {
   // CHECK: ![[A:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "A",
 
   // CHECK-DAG: !DISubprogram(name: "pub_default",{{.*}} line: [[@LINE+1]],{{.*}} flags: DIFlagPrototyped,
   void pub_default();
   // CHECK-DAG: !DIDerivedType(tag: DW_TAG_member, name: "pub_default_static",{{.*}} line: [[@LINE+1]],{{.*}} flags: DIFlagStaticMember)
   static int pub_default_static;
 };
 
 
-// CHECK: !DIDerivedType(tag: DW_TAG_inheritance,{{.*}} baseType: ![[A]],{{.*}} flags: DIFlagPublic)
+// CHECK: !DIDerivedType(tag: DW_TAG_inheritance,{{.*}} baseType: ![[A]],{{.*}} flags: DIFlagPublic, extraData: i32 0)
 class B : public A {
 public:
   // CHECK-DAG: !DISubprogram(name: "pub",{{.*}} line: [[@LINE+1]],{{.*}} flags: DIFlagPublic | DIFlagPrototyped,
   void pub();
   // CHECK-DAG: !DIDerivedType(tag: DW_TAG_member, name: "public_static",{{.*}} line: [[@LINE+1]],{{.*}} flags: DIFlagPublic | DIFlagStaticMember)
   static int public_static;
 protected:
   // CHECK: !DISubprogram(name: "prot",{{.*}} line: [[@LINE+1]],{{.*}} flags: DIFlagProtected | DIFlagPrototyped,

llvm/tools/clang/test/CodeGenCXX/debug-info-ms-vbase.cpp

 // RUN: %clang_cc1 %s -triple=i686-pc-windows-msvc -debug-info-kind=limited -gcodeview -emit-llvm -o - | FileCheck %s
 
 // Tests virtual bases in the MS ABI.
 
 // CHECK: ![[NoPrimaryBase:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "NoPrimaryBase",
 // CHECK-SAME: elements: ![[elements:[0-9]+]]
 
 // CHECK: ![[elements]] = !{![[NoPrimaryBase_base:[0-9]+]]}
 
 // CHECK: ![[NoPrimaryBase_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[NoPrimaryBase]],
-// CHECK-SAME: baseType: ![[HasVirtualMethod:[0-9]+]], offset: 4, flags: DIFlagVirtual)
+// CHECK-SAME: baseType: ![[HasVirtualMethod:[0-9]+]], offset: 4, flags: DIFlagVirtual, extraData: i32 0)
 
 // CHECK: ![[HasVirtualMethod]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "HasVirtualMethod"
 
 // CHECK: ![[HasPrimaryBase:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "HasPrimaryBase",
 // CHECK-SAME: elements: ![[elements:[0-9]+]]
 
 // CHECK: ![[elements]] = !{![[SecondaryVTable_base:[0-9]+]], ![[HasVirtualMethod_base:[0-9]+]], ![[vshape:[0-9]+]]}
 
 // CHECK: ![[SecondaryVTable_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[HasPrimaryBase]],
-// CHECK-SAME: baseType: ![[SecondaryVTable:[0-9]+]], offset: 4, flags: DIFlagVirtual)
+// CHECK-SAME: baseType: ![[SecondaryVTable:[0-9]+]], offset: 4, flags: DIFlagVirtual, extraData: i32 4)
 
 // CHECK: ![[SecondaryVTable]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "SecondaryVTable"
 
-// CHECK: ![[HasVirtualMethod_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[HasPrimaryBase]], baseType: ![[HasVirtualMethod]])
+// CHECK: ![[HasVirtualMethod_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[HasPrimaryBase]], baseType: ![[HasVirtualMethod]], extraData: i32 0)
 
 // CHECK: ![[HasIndirectVirtualBase:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "HasIndirectVirtualBase"
 // CHECK-SAME: elements: ![[elements:[0-9]+]]
 
 // CHECK: !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[HasIndirectVirtualBase]], baseType: ![[HasPrimaryBase]]
 // CHECK-NOT: DIFlagIndirectVirtualBase
 // CHECK-SAME: )
 
 // CHECK: !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[HasIndirectVirtualBase]], baseType: ![[SecondaryVTable]]
 // CHECK-SAME: flags:
 // CHECK-SAME: DIFlagIndirectVirtualBase
 
 // CHECK: ![[DynamicNoVFPtr:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "DynamicNoVFPtr",
 // CHECK-SAME: elements: ![[elements:[0-9]+]]
 
 // CHECK: ![[elements]] = !{![[POD_base:[0-9]+]]}
 
 // CHECK: ![[POD_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[DynamicNoVFPtr]],
-// CHECK-SAME: baseType: ![[POD:[0-9]+]], offset: 4, flags: DIFlagVirtual)
+// CHECK-SAME: baseType: ![[POD:[0-9]+]], offset: 4, flags: DIFlagVirtual, extraData: i32 0)
 
 // CHECK: ![[POD]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "POD"
 
 struct POD { int pod; };
 
 struct DynamicNoVFPtr : virtual POD { };
 
 DynamicNoVFPtr dynamic_no_vfptr;