Add signbit property to frange to better model signed zeros.

As discussed here:

	https://gcc.gnu.org/pipermail/gcc-patches/2022-August/600656.html

This adds an frange property to keep track of the sign bit.  We keep
it updated at all times, but we don't use it make any decisions when
!HONOR_SIGNED_ZEROS.

With this property we can now query the range for the appropriate sign
with frange::get_signbit ().  Possible values are yes, no, and unknown.

gcc/ChangeLog:

	* range-op-float.cc (foperator_equal::op1_range): Do not copy sign
	bit.
	(foperator_not_equal::op1_range): Same.
	* value-query.cc (range_query::get_tree_range): Set sign bit.
	* value-range-pretty-print.cc (vrange_printer::visit): Dump sign bit.
	* value-range.cc (frange::set_signbit): New.
	(frange::set): Adjust for sign bit.
	(frange::normalize_kind): Same.
	(frange::union_): Remove useless comment.
	(frange::intersect): Same.
	(frange::contains_p): Adjust for sign bit.
	(frange::singleton_p): Same.
	(frange::verify_range): Same.
	(range_tests_signbit): New tests.
	(range_tests_floats): Call range_tests_signbit.
	* value-range.h (class frange_props): Add signbit
	(class frange): Same.

1 files changed, 4 insertions, 0 deletions

diff --git a/gcc/value-range.h b/gcc/value-range.h
index f7f3665..3767bd1 100644
--- a/gcc/value-range.h
+++ b/gcc/value-range.h
@@ -314,10 +314,12 @@ public:
   bool intersect (const frange_props &other);
   bool operator== (const frange_props &other) const;
   FP_PROP_ACCESSOR(nan)
+  FP_PROP_ACCESSOR(signbit)
 private:
   union {
     struct {
       unsigned char nan : 2;
+      unsigned char signbit : 2;
     } bits;
     unsigned char bytes;
   } u;
@@ -364,6 +366,8 @@ public:
   // Accessors for FP properties.
   fp_prop get_nan () const { return m_props.get_nan (); }
   void set_nan (fp_prop::kind f);
+  fp_prop get_signbit () const { return m_props.get_signbit (); }
+  void set_signbit (fp_prop::kind);
 private:
   void verify_range ();
   bool normalize_kind ();