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, 19 insertions, 8 deletions

diff --git a/gcc/value-query.cc b/gcc/value-query.cc
index 4637fb4..201f679 100644
--- a/gcc/value-query.cc
+++ b/gcc/value-query.cc
@@ -217,14 +217,25 @@ range_query::get_tree_range (vrange &r, tree expr, gimple *stmt)
       return true;
 
     case REAL_CST:
-      if (TREE_OVERFLOW_P (expr))
-	expr = drop_tree_overflow (expr);
-      r.set (expr, expr);
-      if (real_isnan (TREE_REAL_CST_PTR (expr)))
-	as_a <frange> (r).set_nan (fp_prop::YES);
-      else
-	as_a <frange> (r).set_nan (fp_prop::NO);
-      return true;
+      {
+	if (TREE_OVERFLOW_P (expr))
+	  expr = drop_tree_overflow (expr);
+
+	frange &f = as_a <frange> (r);
+	f.set (expr, expr);
+
+	// Singletons from the tree world have known properties.
+	REAL_VALUE_TYPE *rv = TREE_REAL_CST_PTR (expr);
+	if (real_isnan (rv))
+	  f.set_nan (fp_prop::YES);
+	else
+	  f.set_nan (fp_prop::NO);
+	if (real_isneg (rv))
+	  f.set_signbit (fp_prop::YES);
+	else
+	  f.set_signbit (fp_prop::NO);
+	return true;
+      }
 
     case SSA_NAME:
       gimple_range_global (r, expr);