Resolution of B-2 not reflected in B-6 (aka covariant returns)

[Jason Merrill]

>>>>> Jim Dehnert <dehnert at baalbek.engr.sgi.com> writes:

 > I think this can be dealt with by the following rule:

 >   The adjusting entrypoints referenced by vtable entries in secondary
 >   vtables must adjust both the this pointer and the covariant return
 >   pointer (if necessary).  If a derived class and its primary base
 >   share a vtable, and the derived class overrides a virtual function in
 >   the primary base's primary vtable with a different return type, then
 >   the shared vtable entry adjusts the return type to that required by
 >   the base class, and a second entry is allocated in the derived type's
 >   vtable (according to the position rules for any vfunc added by the
 >   derived class) for the overriding function, which adjusts neither
 >   this nor the return type.

 > Note that this rule does not provide what I originally assumed was
 > meant by "multiple entries for covariant returns," as it makes use of
 > the multiple entries already present in secondary vtables when it can.

I think that is what was meant.  To restate:

  When a virtual function is declared in a class, it gets a new vtable slot
  unless it overrides a function from the primary base and conversion
  between the two return types does not require an adjustment.

It seems unnecessary to force a new entry if the return types are related
by single inheritance.

Jason