https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109008
--- Comment #27 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #21)
> So without messing with real.cc to try exposing 0.5ulp adjustments for GCC
> 13 I'd simply do something like the following:
>
> diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
> index ff42b95de4f..1ae68503664 100644
> --- a/gcc/range-op-float.cc
> +++ b/gcc/range-op-float.cc
> @@ -2214,7 +2214,26 @@ public:
> range_op_handler minus (MINUS_EXPR, type);
> if (!minus)
> return false;
> - return float_binary_op_range_finish (minus.fold_range (r, type, lhs,
> op2),
> + /* The forward operation is
> + lhs = r + op2
> + where the result is +-0.5ulp of lhs before rounding. For the
> + reverse operation we need the lhs range before rounding, so
> + conservatively use nextafter on it.
> + ??? REAL_VALUE_TYPE could handle this more precisely if we
> + make sure to not round the inputs for the format before the
> + real_operation is carried out and when we can properly round
> + towards +-Inf for the lower/upper bounds. */
> + frange wlhs (lhs);
> + if (!lhs.known_isnan ())
> + {
> + REAL_VALUE_TYPE lhsl = lhs.lower_bound ();
> + frange_nextafter (TYPE_MODE (type), lhsl, dconstninf);
> + REAL_VALUE_TYPE lhsu = lhs.upper_bound ();
> + frange_nextafter (TYPE_MODE (type), lhsu, dconstinf);
> + wlhs.set (type, lhsl, lhsu);
> + wlhs.union_ (lhs); /* Copy NaN state. */
> + }
> + return float_binary_op_range_finish (minus.fold_range (r, type, wlhs,
> op2),
> r, type, lhs);
> }
> virtual bool op2_range (frange &r, tree type,
Could we abstract this into an inline function until this could be properly
implemented in real.cc?
