objects_must_conflict_p

[Richard Kenner]

    Then a (non-temporary) 'struct a_iterator1' object is created:
    allocated on the stack and constructed, so 'adaptor' is
    assigned. 'struct iterator1' and 'struct a_iterator1' conflicts
    according to objects_must_conflict_p, because the latter is a
    supertype of the former. 

Yuck!  It looks like we have to say they only are guaranteed to conflict
if they have the *same* alias set.