is_floating - RTTI specification.

[Jason Merrill]

>>>>> Coleen Phillimore <coleen at zko.dec.com> writes:

 > Well, it depends on if you're representing both indirect and direct base
 > classes in the RTTI.  If you're representing both, there's no advantage.
 > But if you're representing only direct and then using the RTTI for the
 > direct base classes to get to indirect classes, you can't put absolute
 > offsets to "floating"/virtual subobjects, 'cause they, uh, well, float.
 > The latter is how our EDG compiler works today.  Only representing
 > direct base clases saves space, but costs time in dynamic cast and
 > exception handling.

I feel pretty strongly that we should only represent direct base classes.
We want to minimize the impact of RTTI and EH on code that doesn't use it;
making throws and dynamic_cast a bit slower doesn't seem like a problem to
me.

Jason