RTTI updates

[Nathan Sidwell]

Jim Dehnert wrote:
[rtti updates]

Thanks for the update, it all looks good.

Some pedant points.
* (7b) The description of __si_type_info still does not say the base must
be public and at offset zero.
* (7c) The description of __class_type_info still says `containing (directly
or indirectly)', Jason's mail indicates the intention is `containing directly'
* (7c) The vmi_flags should probably indicate they refer to direct and indirect
bases.

And a more significant one.
* (7c) I see the diamond shaped flag has been added, what about the non-diamond
shaped multiple sub-object? That too is important for dynamic cast and base
class catching.

For instance, in dynamic cast, when we locate an instance of the target class
the following cases can be considered
1) The complete class has no multiple sub-objects. There cannot be another
instance of the target class in the heirarchy, so we're done.
2) The complete class is diamond-shaped, but has no non-diamond shaped multiple
base object. There will be no other instance of the target class, but the target
may be reachable via another path. That other path could be publicly accessible,
so if we've found a private access to the target keep looking, otherwise we're
done.
3) The complete class has non-diamond shaped multiple base object, but is not
diamond shaped. There may be other instances of the target class, which could
ambiguate the dynamic cast. The other instances cannot share base objects. If the
src sub object is within the located target, this is unambiguous, so we're done.
Otherwise keep looking.
4) The complete class has non-diamond shaped multiple base object, and is
diamond shaped too. There may be other instances of the target class, which
could share base objects. Keep looking.

Similar cases arise in catch matching on casting derived to base.

Without the non-diamond shaped multiple subobject flag, both dynamic cast
and catch matching must take paths 3 or 4, which are more work and I'd hazard
less common.

Maybe there was insufficient time to discus this at the meeting. Just want to
make sure it's not forgotten.

nathan
-- 
Dr Nathan Sidwell :: Computer Science Department :: Bristol University
Never hand someone a gun unless you are sure where they will point it
nathan at acm.org  http://www.cs.bris.ac.uk/~nathan/  nathan at cs.bris.ac.uk