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

[Mikael Morin]

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);