[gcc r13-2741] frange::set_nonnegative should not contain -NAN.

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

https://gcc.gnu.org/g:10d6109fe183d984a0377a7afe2854a0d794ebeb

commit r13-2741-g10d6109fe183d984a0377a7afe2854a0d794ebeb
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Mon Sep 19 09:59:01 2022 +0200

    frange::set_nonnegative should not contain -NAN.
    
    A specifically nonnegative range should not contain -NAN, otherwise
    signbit_p() would return false, because we'd be unsure of the sign.
    
            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.

Diff:
---
 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 a8e3bb39bab..dc42b6d3120 100644
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -775,6 +775,10 @@ 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
@@ -3823,6 +3827,11 @@ 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 795b1f00fdc..7d5584a9294 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
@@ -1099,6 +1100,19 @@ 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