On Mon, Sep 5, 2022 at 11:18 AM Richard Biener <richard.guent...@gmail.com> wrote: > > On Mon, Sep 5, 2022 at 11:12 AM Aldy Hernandez <al...@redhat.com> wrote: > > > > 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. > > > > Right. I don't print any of the "maybe" properties, just if they're > > definitely set or definitely clear. I'm open to suggestions as to how > > to display them. Perhaps NAN, !NAN, ?NAN. > > There's no NAN tristate. Your "definitely NAN" would be simply > ][ NAN, that is, the value range only contains NAN. Your !NAN > is <whatever range> and non NAN. Likewise for the sign, the > range either includes -NAN and NAN or one or none of those. > For signed zeros you either have [-0, upper-bound] or [0, upper-bound] > where it either includes both -0 and 0 or just one of them
But there is a tristate. We may definitely have a NAN, definitely not have a NAN, or the state of the NAN is unknown. Say [3,5] ?NAN. That's [3,5] with the possibility of a NAN. On the true side of x >= 5.0, we'd have [5.0, INF] !NAN. On the false side we'd have [-INF, 5.0] ?NAN. With this representation we can fold __builtin_isnan() even on an unknown value... say on the true side of x == y we know that both x and y cannot be NANs...but on the false side we know nothing so there is the possibility of a NAN. I do like your idea for signed zeros. I think I could make it work and get rid of the sign bit. Aldy > > > I'm mostly worried about removing a NAN from the IL that was going to > > signal, or some such. While I agree with you Richard, I just want to > > make real sure, because getting something wrong in the frange or > > range-ops bowels means the problem becomes pervasive to all of ranger > > ...and threader...and loop ch...and vrp, etc etc. I just want to take > > more time to test things. I promise it won't stay varying too long. > > There's sNANs and qNANs, but I think for value-ranges we should > concern ourselves only with qNANs for now and leave sNANs VARYING. > All operations only ever produce qNANs (loads can produce sNANs). > > Richard. > > > Aldy > > >
