On Mon, Sep 5, 2022 at 11:06 AM Jakub Jelinek <ja...@redhat.com> wrote: > > 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.
Uh, that's confusing. So [3, 5] U maybe NAN intersected with ][ NAN is ][ NAN. [3, 5] !NAN intersected with ][ NAN is ][ !NAN. In fact [3, 5] U maybe NAN is just [3, 5] U NAN, there's no "maybe" ranges, if the value may be NAN then NAN is in the value-range. So it's either [3, 5] U NAN or [3, 5] (without U NAN). Richard. > > Jakub >
