[gcc r13-2394] Do not clobber signbit when unioning a NAN.

[Aldy Hernandez <aldyh@gcc.gnu.org>]

https://gcc.gnu.org/g:8293a9632c46c8f3f9d531c09194aa8738944927

commit r13-2394-g8293a9632c46c8f3f9d531c09194aa8738944927
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Sun Sep 4 08:00:02 2022 +0200

    Do not clobber signbit when unioning a NAN.
    
    When unioning a known NAN and something else, we're dropping the
    properties of the NAN, particularly the sign.  This fixes the
    oversight.
    
    With this patch, we should be keeping the sign bit up to date, even in
    the presence of NANs.
    
    gcc/ChangeLog:
    
            * value-range.cc (frange::union_): Do not drop properties when
            unioning a NAN with something else.
            (range_tests_signed_zeros): Add tests.

Diff:
---
 gcc/value-range.cc | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index a1c29f7bd0b..c9f42fe272c 100644
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -475,19 +475,25 @@ frange::union_ (const vrange &v)
       return true;
     }
 
-  // If one side has a NAN, the union is just the other side plus the
-  // NAN bit.
+  // If one side has a NAN, the union is the other side, plus the union
+  // of the properties and the possibility of a NAN.
   if (get_nan ().yes_p ())
     {
+      frange_props save = m_props;
       *this = r;
-      // NOP if NAN already set.
+      m_props = save;
+      m_props.union_ (r.m_props);
       set_nan (fp_prop::VARYING);
+      if (flag_checking)
+	verify_range ();
       return true;
     }
   if (r.get_nan ().yes_p ())
     {
-      // NOP if NAN already set.
+      m_props.union_ (r.m_props);
       set_nan (fp_prop::VARYING);
+      if (flag_checking)
+	verify_range ();
       return true;
     }
 
@@ -3676,6 +3682,7 @@ range_tests_signed_zeros ()
 {
   tree zero = build_zero_cst (float_type_node);
   tree neg_zero = fold_build1 (NEGATE_EXPR, float_type_node, zero);
+  REAL_VALUE_TYPE q, r;
   frange r0, r1;
 
   // Since -0.0 == +0.0, a range of [-0.0, -0.0] should contain +0.0
@@ -3711,6 +3718,16 @@ range_tests_signed_zeros ()
   r1.set_signbit (fp_prop::YES);
   r0.union_ (r1);
   ASSERT_TRUE (r0.zero_p () && r0.get_signbit ().varying_p ());
+
+  // NAN U [5,6] should be [5,6] with no sign info.
+  r0 = frange_nan (float_type_node);
+  r1 = frange_float ("5", "6");
+  r0.union_ (r1);
+  real_from_string (&q, "5");
+  real_from_string (&r, "6");
+  ASSERT_TRUE (real_identical (&q, &r0.lower_bound ()));
+  ASSERT_TRUE (real_identical (&r, &r0.upper_bound ()));
+  ASSERT_TRUE (r0.get_signbit ().varying_p ());
 }
 
 static void