Re: [PATCH][RFC] Step 1 to a middle-end type-system

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 6/24/07, Richard Guenther <richard.guenther@gmail.com> wrote:
> On 6/24/07, Eric Botcazou <ebotcazou@libertysurf.fr> wrote:
> > >   /* Return true if the conversion from INNER_TYPE to OUTER_TYPE is
> > > !    explicitly, otherwise return false.
> > > !    This function implicitly defines the middle-end type system.  The
> > > !    following invariants shall be fulfilled:
> > > !
> > > !      1) type_conversion_needed_p is transitive.
> > > !     If a < b and b < c then a < c.
> >
> > I don't think this is true, take a = c = int and b = char.  Which would
> > suggest that the reverse form useless_type_conversion is probably easier
> > to deal with, conceptually.
>
> I don't understand.  For a = c = int and b = char neither a < b nor b < c.

Oh, I see.  The above was written at the time the predicate was named
useless_type_conversion_p -- of course transitivity only olds for useless,
not for needed.  Hmm, so maybe a bad name after all.

Richard.