On Tue, Aug 30, 2022 at 5:43 PM Aldy Hernandez via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Previously [5,6] U NAN would just drop to VARYING. With this patch,
> the resulting range becomes [5,6] with the NAN bit set to unknown.
>
> [I still have yet to decide what to do with intersections. ISTM, the
> intersection of a known NAN with anything else should be a NAN, but it
> could also be undefined (the empty set). I'll have to run some tests
> and see. Currently, we drop to VARYING cause well... it's always safe
> to give up;-).]
Giving up in too many places will hide bugs in others for too long ...
> gcc/ChangeLog:
>
> * value-range.cc (early_nan_resolve): Change comment.
> (frange::union_): Handle union when one side is a NAN.
> (range_tests_nan): Add tests for NAN union.
> ---
> gcc/value-range.cc | 44 ++++++++++++++++++++++++++++++++++----------
> 1 file changed, 34 insertions(+), 10 deletions(-)
>
> diff --git a/gcc/value-range.cc b/gcc/value-range.cc
> index b6d6c62c06c..473139c6dbd 100644
> --- a/gcc/value-range.cc
> +++ b/gcc/value-range.cc
> @@ -403,7 +403,7 @@ early_nan_resolve (frange &r, const frange &other)
> // There's nothing to do for both NANs.
> if (r.get_nan ().yes_p () == other.get_nan ().yes_p ())
> return false;
> - // But only one NAN complicates things.
> + // ?? Perhaps the intersection of a NAN and anything is a NAN ??.
> r.set_varying (r.type ());
> return true;
> }
> @@ -420,10 +420,22 @@ frange::union_ (const vrange &v)
> *this = r;
> return true;
> }
> - // ?? We could do better here. [5,6] U NAN should be [5,6] with the
> - // NAN maybe bits set. For now, this is conservatively correct.
> - if (get_nan ().yes_p () || r.get_nan ().yes_p ())
> - return early_nan_resolve (*this, r);
> +
> + // If one side has a NAN, the union is just the other side plus the
> + // NAN bit.
> + if (get_nan ().yes_p ())
> + {
> + *this = r;
> + // NOP if NAN already set.
> + set_nan (fp_prop::VARYING);
> + return true;
> + }
> + if (r.get_nan ().yes_p ())
> + {
> + // NOP if NAN already set.
> + set_nan (fp_prop::VARYING);
> + return true;
> + }
>
> bool changed = m_props.union_ (r.m_props);
>
> @@ -3520,6 +3532,7 @@ static void
> range_tests_nan ()
> {
> frange r0, r1;
> + REAL_VALUE_TYPE q, r;
>
> // Equal ranges but with differing NAN bits are not equal.
> r1 = frange_float ("10", "12");
> @@ -3537,13 +3550,24 @@ range_tests_nan ()
> ASSERT_FALSE (r0 == r0);
> ASSERT_TRUE (r0 != r0);
>
> - // Make sure that combining NAN and INF doesn't give any crazy results.
> + // [5,6] U NAN is [5,6] with an unknown NAN bit.
> + r0 = frange_float ("5", "6");
> + r0.set_nan (fp_prop::NO);
> + r1 = frange_nan (float_type_node);
> + r0.union_ (r1);
> + real_from_string (&q, "5");
> + real_from_string (&r, "6");
> + ASSERT_TRUE (real_identical (&q, &r0.lower_bound ()));
> + ASSERT_TRUE (real_identical (&r, &r0.upper_bound ()));
> + ASSERT_TRUE (r0.get_nan ().varying_p ());
> +
> + // NAN U NAN = NAN
> r0 = frange_nan (float_type_node);
> - ASSERT_TRUE (r0.get_nan ().yes_p ());
> - r1 = frange_float ("+Inf", "+Inf");
> + r1 = frange_nan (float_type_node);
> r0.union_ (r1);
> - // [INF, INF] U NAN = VARYING
> - ASSERT_TRUE (r0.varying_p ());
> + ASSERT_TRUE (real_isnan (&r0.lower_bound ()));
> + ASSERT_TRUE (real_isnan (&r1.upper_bound ()));
> + ASSERT_TRUE (r0.get_nan ().yes_p ());
>
> // [INF, INF] ^ NAN = VARYING
> r0 = frange_nan (float_type_node);
> --
> 2.37.1
>
