Strange unreachable error when mixing base class with other classes w/ function override.

[AfflatusX]

It's hard to describe the issue... so I created a repro here: https://webassembly.studio/?f=025lli7p08dc

The bug requires following conditions to be met:

1. a base class type needs to be used when creating the instance. In the example, that's line 38. If we create concrete class type, no exception.
2. we need 2 separate classes, where one inherit another. Base should have a virtual function defined, and Child should overload that. See line 11 and line 1.
3. invoke the function from a function in a class created in 1. See line 31.

Running the code should yield unreachable exception while the code above is perfectly legal.

I feel the class/interface implementation of AS isn't complete, and it's hard to debug these issues since it will usually just say "unreachable".

[MaxGraey]

Simplified example a bit:
https://webassembly.studio/?f=usrhhehggba

[dcodeIO]

Looking at the generated code, for some reason A#callImpl's virtual stub reads like this

 (func $A#callImpl@virtual (param $0 i32) (result i32)
  unreachable
 )

which is missing the B#callImpl overload. In fact, B#callImpl is not part of the binary, indicating that some sort of tree-shaking is going on, missing that it may still be called.