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Re: tree_ssa_useless_type_conversions
- From: law at redhat dot com
- To: Jan Hubicka <jh at suse dot cz>
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 11 Nov 2003 14:05:51 -0700
- Subject: Re: tree_ssa_useless_type_conversions
- Reply-to: law at redhat dot com
In message <20031111085648.GA1729@kam.mff.cuni.cz>, Jan Hubicka writes:
>I am having problem to think of how to do type checking in such a
>relaxed typing system. Gimple specifies that types must match.
I think we need to update the gimple documentation. We have relaxed
the requirement that types must match exactly.
>If I
>write tree_ssa_types_compatible_p predicate that duplicate the code of
>useless_type_conversion, I run into proplem that the function is not
>transitive nor symmetric and thus we do not produce equivalence classes.
Yup. There are cases when it can't be symmetric, particularly in regards
to casting pointer types.
>We may change type twice, both times doing allowed useless conversion
>and end up with non-useless conversion.
That would be a bug. Specifics please (ie compilable code).
jeff