Re: Virtual Mem Func Ptr Call Fails When Base Class Has No Vtable

["Martin v. Loewis" <martin at mira dot isdn dot cs dot tu-berlin dot de>]

> Err...  The C++ Standard says [expr.static.cast]:

I see. Learn something new about C++ every day :-)

> Since the class B is a base of the class containing the original
> member, the old-style cast should succeed as a static_cast, and should
> not invoke undefined behavior.

The bug appears is that g++ just *knows* that the pointer-to-member
won't call a virtual function, if the class doesn't have virtual
functions. If the example is right, this assumption is wrong. Removing
the fragment

      if (TYPE_SIZE (basetype) != NULL_TREE
	  && ! TYPE_VIRTUAL_P (basetype))
	/* If basetype doesn't have virtual functions, don't emit code to
	   handle that case.  */
	e1 = e3;
      else

from typeck.c fixes the bug.

> I seem to recall some wording in the Standard (or some earlier WP)
> that would make the *use* of this pointer-to-member undefined unless
> it was declared as virtual in the case class, but I can't find it any
> more.  Can anybody?

I couldn't. Furthermore, I could not even find the statement that a
pointer-to-member call should consider virtuality. If somebody tells
me where that is, I produce a patch.

It would be a pity, though - this is such a nice optimization :-)

Regards,
Martin