Re: [PATCH] Rewrite NAN and sign handling in frange

[Mikael Morin <morin-mikael@orange.fr>]

Hello,

Le 16/09/2022 à 15:26, Aldy Hernandez via Gcc-patches a écrit :
> diff --git a/gcc/value-range.cc b/gcc/value-range.cc
> index d759fcf178c..55a216efd8b 100644
> --- a/gcc/value-range.cc
> +++ b/gcc/value-range.cc
> @@ -617,21 +602,24 @@ frange::contains_p (tree cst) const
>    if (varying_p ())
>      return true;
>  
  (...)
>  
>    if (real_compare (GE_EXPR, rv, &m_min) && real_compare (LE_EXPR, rv, &m_max))
>      {
> +      // Make sure the signs are equal for signed zeros.
>        if (HONOR_SIGNED_ZEROS (m_type) && real_iszero (rv))
> -	{
> -	  // FIXME: This is still using get_signbit() instead of
> -	  // known_signbit() because the latter bails on possible NANs
> -	  // (for now).
> -	  if (get_signbit ().yes_p ())
> -	    return real_isneg (rv);
> -	  else if (get_signbit ().no_p ())
> -	    return !real_isneg (rv);
> -	  else
> -	    return true;
> -	}
> +	return m_min.sign == m_max.sign && m_min.sign == rv->sign;
>        return true;
>      }
>    return false;

It seems that this won't report any range with mismatching bound signs 
as containing zero.
Maybe a selftest explains it better: the following fails.

diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index 9ca442478c9..8fc909171bc 100644
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -3780,6 +3780,14 @@ range_tests_signed_zeros ()
    ASSERT_TRUE (r0.contains_p (neg_zero));
    ASSERT_FALSE (r0.contains_p (zero));

+  r0 = frange_float ("-3", "5");
+  ASSERT_TRUE (r0.contains_p (neg_zero));
+  ASSERT_TRUE (r0.contains_p (zero));
+
+  r0 = frange (neg_zero, zero);
+  ASSERT_TRUE (r0.contains_p (neg_zero));
+  ASSERT_TRUE (r0.contains_p (zero));
+
    // The intersection of zeros that differ in sign is a NAN (or
    // undefined if not honoring NANs).
    r0 = frange (neg_zero, neg_zero);