https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109008
--- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> ---
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,
