gcc 3.0.1 & C++ ABI issues

[Joe Buck]

Sigh, the quotes below are pretty messy, but ...

> >>>>> "Nathan" == Nathan Sidwell <nathan@codesourcery.com> writes:
> 
> > Jason Merrill wrote:
> >> 
> >> >>>>> "Mark" == Mark Mitchell <mark@codesourcery.com> writes:
> >> 
> >> > What do you think we should do in the 3.0.1 time frame?  Can we get
> >> > a reasonably safe patch that will fix the correctness issue and
> >> > not cause the (minor) pessimization?  (This would clearly be the
> >> > ideal solution.)
> >> 
> >> I think a patch that just disables the optimization for the case of copying
> >> an lvalue of empty class type would be fine for 3.0.1.
> 
> > This is insufficient. I attach a test case where we assign a
> > temporary into an empy base, and clobber what it overlays.

Jason:
> Yes, your change to the assignment case is good; I was only thinking about
> initialization.  The case I still want to optimize is the case of
> initializing an empty class object from a temporary.

Our STL implementation has lots of code where a dummy argument whose type
is an empty class is used to specialize templates.  Are we getting
pessimization because of this?