On Mon, Sep 19, 2022 at 9:59 AM Aldy Hernandez <al...@redhat.com> wrote:
>
> ISTM that a specifically nonnegative range should not contain -NAN,
> otherwise signbit_p() would return false, because we'd be unsure of the
> sign.
>
> Do y'all agree?
what tree_expr_nonnegative_p actually means isn't 100% clear. For REAL_CST
it actually looks at the sign-bit but we have
(simplify
/* copysign(x,y) -> fabs(x) if y is nonnegative. */
(COPYSIGN_ALL @0 tree_expr_nonnegative_p@1)
(abs @0))
is abs (@0) OK for sNaNs and -NaN/+NaN?
And we have
/* Convert abs[u] (X) where X is nonnegative -> (X). */
(simplify
(abs tree_expr_nonnegative_p@0)
@0)
where at least sNaN -> qNaN would be dropped?
And of course
(simplify
/* signbit(x) -> 0 if x is nonnegative. */
(SIGNBIT tree_expr_nonnegative_p@0)
{ integer_zero_node; })
that is, is tree_expr_nonnegative_p actually tree_expr_sign or
does tree_expr_nonnegative (x) mean x >= (typeof(X)) 0
or !(x < (typeof(X))0)?
That said, 'set_nonnegative' could be interpreted to be without
NaNs?
Richard.
> PR 68097/tree-optimization
>
> gcc/ChangeLog:
>
> * value-range.cc (frange::set_nonnegative): Set +NAN.
> (range_tests_signed_zeros): New test.
> * value-range.h (frange::update_nan): New overload to set NAN sign.
> ---
> gcc/value-range.cc | 9 +++++++++
> gcc/value-range.h | 14 ++++++++++++++
> 2 files changed, 23 insertions(+)
>
> diff --git a/gcc/value-range.cc b/gcc/value-range.cc
> index 67d5d7fa90f..e432ec8b525 100644
> --- a/gcc/value-range.cc
> +++ b/gcc/value-range.cc
> @@ -752,6 +752,10 @@ void
> frange::set_nonnegative (tree type)
> {
> set (type, dconst0, dconstinf);
> +
> + // Set +NAN as the only possibility.
> + if (HONOR_NANS (type))
> + update_nan (/*sign=*/0);
> }
>
> // Here we copy between any two irange's. The ranges can be legacy or
> @@ -3800,6 +3804,11 @@ range_tests_signed_zeros ()
> r1.update_nan ();
> r0.intersect (r1);
> ASSERT_TRUE (r0.known_isnan ());
> +
> + r0.set_nonnegative (float_type_node);
> + ASSERT_TRUE (r0.signbit_p (signbit) && !signbit);
> + if (HONOR_NANS (float_type_node))
> + ASSERT_TRUE (r0.maybe_isnan ());
> }
>
> static void
> diff --git a/gcc/value-range.h b/gcc/value-range.h
> index 3a401f3e4e2..5b261d4f46a 100644
> --- a/gcc/value-range.h
> +++ b/gcc/value-range.h
> @@ -312,6 +312,7 @@ public:
> const REAL_VALUE_TYPE &lower_bound () const;
> const REAL_VALUE_TYPE &upper_bound () const;
> void update_nan ();
> + void update_nan (bool sign);
> void clear_nan ();
>
> // fpclassify like API
> @@ -1098,6 +1099,19 @@ frange::update_nan ()
> verify_range ();
> }
>
> +// Like above, but set the sign of the NAN.
> +
> +inline void
> +frange::update_nan (bool sign)
> +{
> + gcc_checking_assert (!undefined_p ());
> + m_pos_nan = !sign;
> + m_neg_nan = sign;
> + normalize_kind ();
> + if (flag_checking)
> + verify_range ();
> +}
> +
> // Clear the NAN bit and adjust the range.
>
> inline void
> --
> 2.37.1
>
