[COMMITTED] Add method to query the sign of a NAN.

[Aldy Hernandez via Gcc-patches]

In writing some range-op entries I noticed we don't have a way to
query the sign of the NAN in a range, unless the range only contains
NAN, in which case you can just use frange::signbit_p.  This patch
adds a method that returns TRUE if there exists the possiblity of a
NAN and we know its sign.

gcc/ChangeLog:

        * value-range.h (frange::nan_signbit_p): New.
---
 gcc/value-range.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/gcc/value-range.h b/gcc/value-range.h
index cb5e9d0522c..60b989b2b50 100644
--- a/gcc/value-range.h
+++ b/gcc/value-range.h
@@ -328,6 +328,7 @@ public:
   bool maybe_isnan (bool sign) const;
   bool maybe_isinf () const;
   bool signbit_p (bool &signbit) const;
+  bool nan_signbit_p (bool &signbit) const;
 private:
   void verify_range ();
   bool normalize_kind ();
@@ -1358,4 +1359,20 @@ frange::signbit_p (bool &signbit) const
   return false;
 }
 
+// If range has a NAN with a known sign, set it in SIGNBIT and return
+// TRUE.
+
+inline bool
+frange::nan_signbit_p (bool &signbit) const
+{
+  if (undefined_p ())
+    return false;
+
+  if (m_pos_nan == m_neg_nan)
+    return false;
+
+  signbit = m_neg_nan;
+  return true;
+}
+
 #endif // GCC_VALUE_RANGE_H
-- 
2.37.3