On Mon, Sep 05, 2022 at 11:00:54AM +0200, Richard Biener wrote:
> On Mon, Sep 5, 2022 at 8:24 AM Aldy Hernandez via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > Intersecting two ranges where one is a NAN is keeping the sign bit of
> > the NAN range. This is not correct as the sign bits may not match.
> >
> > I think the only time we're absolutely sure about the intersection of
> > a NAN and something else, is when both are a NAN with exactly the same
> > properties (sign bit). If we're intersecting two NANs of differing
> > sign, we can decide later whether that's undefined or just a NAN with
> > no known sign. For now I've done the latter.
> >
> > I'm still mentally working on intersections involving NANs, especially
> > if we want to keep track of signbits. For now, let's be extra careful
> > and only do things we're absolutely sure about.
> >
> > Later we may want to fold the intersect of [NAN,NAN] and say [3,5]
> > with the posibility of NAN, to a NAN, but I'm not 100% sure.
>
> The intersection of [NAN, NAN] and [3, 5] is empty. The intersection
> of [NAN, NAN] and VARYING is [NAN, NAN].
I think [3.0, 5.0] printed that way currently means U maybe NAN,
it would be [3.0, 5.0] !NAN if it was known not to be NAN.
Jakub
