objects_must_conflict_p

[Eric Botcazou]

> I think you're right.  It would be enough to check if the alias sets have
> a common subset.

Are you sure this would be sufficient? Both aggregates can have an 'int' 
field and this won't prevent problems between 'int' and 'double' fields.

> In which case, we essentially *never* share stack slots since they aren't
> allocated for scalars.

Hum... yes, you're right, this seems to be a bit drastic.

For arrays, we can obviously do better. For records and unions, we could 
check that every single member of the first conflicts with every single 
member of the second, but this would be costly.

Btw, why did you choose to always return 0 for scalar vs aggregate? In this 
case, I think that alias_sets_conflict_p is the right criterion.

-- 
Eric Botcazou