Covariant returns

[Mark Mitchell]

Although the closed issues list discusses covariant returns, the ABI
document itself does not.  It looks like we agreed on providing
alternate entry points for non-trivial covariant returns.  In that
case, we need to specify the order in the vtabe in which such entries
appear.  Since we also provide a copy of a virtual function in the
primary vtable when a derived class orverrides a virtual function from
a secondary base, we need to know whether to make copies of all the
entry points, or just the one with the same signature as that provided
in the derived class.  There also need to be vcall offsets for all of
the covariant returns.  Other issues?

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Mark Mitchell                   mark at codesourcery.com
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