On recent trunk:

> $ cat test.cc
> struct Color {};
> template<typename> struct SharedPtr {};
> struct Canvas {
>     virtual ~Canvas() {}
>     virtual void getClip() = 0;
>     virtual SharedPtr<Color> createColor() = 0;
> };
> struct BitmapCanvas: virtual Canvas {};
> struct ImplCanvas: virtual Canvas {
>     virtual ~ImplCanvas();
>     void getClip() override;
>     SharedPtr<Color> createColor() override;
> };
> struct ImplBitmapCanvas: virtual BitmapCanvas, virtual ImplCanvas {
>     virtual ~ImplBitmapCanvas();
> };
> ImplBitmapCanvas::~ImplBitmapCanvas() {}
> ImplBitmapCanvas c;

> $ clang-cl -c test.cc

> $ llvm-nm test.obj | grep -F '?getClip@ImplCanvas@@$'
> 00000000 T ?getClip@ImplCanvas@@$4PPPPPPPM@A@EAAXXZ
> 00000000 T ?getClip@ImplCanvas@@$R4BA@M@PPPPPPPM@BA@EAAXXZ

> $ llvm-nm test.obj | grep -F '?createColor@ImplCanvas@@$'
>          U ?createColor@ImplCanvas@@$4PPPPPPPM@A@EAA?AU?$SharedPtr@UColor@@@@XZ
>          U ?createColor@ImplCanvas@@$R4BA@M@PPPPPPPM@BA@EAA?AU?$SharedPtr@UColor@@@@XZ

The vtordisp thunks for getClip are emitted, while those for createColor are erroneously missing.

The reason is that CodeGenVTabels::maybeEmitThunkForVtable (lib/CodeGen/CGVtables.cpp) returns early if !isFuncTypeConvertible, which hits here as the ClassTemplateSpecializationDecl for SharedPtr<Color> is !isCompleteDefinition, as there's no code in Sema that happens to call Sema::RequireCompleteType -> Sema::InstantiateClassTemplateSpecialization on it.