From 8293a9632c46c8f3f9d531c09194aa8738944927 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Sun, 4 Sep 2022 08:00:02 +0200
Subject: [PATCH] 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.
---
 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