frange: Fix up foperator_{,not_}equal::fold_range for signed zeros [PR108540]

The following testcases are miscompiled, because threader sees some
SSA_NAME would have -0.0 value and when computing range of SSA_NAME == 0.0
foperator_equal::fold_range sees one operand has [-0.0, -0.0] singleton
range, the other [0.0, 0.0], they aren't equal (frange operator== uses
real_identical etc. rather than real comparisons) and so it thinks they
compare unequal.  With signed zeros -0.0 == 0.0 is true though, so we
need to special case the both ranges singleton code.
Similarly, if we see op1 range being say [-42.0, -0.0] and op2 range
[0.0, 42.0], we'd check that the intersection of the two ranges is empty
(that is correct) and fold the result of == between such operands to
[0, 0] which is wrong, because -0.0 == 0.0, it needs to be [0, 1].
Similarly for foperator_not_equal::fold_range.

2023-01-26  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108540
	* range-op-float.cc (foperator_equal::fold_range): If both op1 and op2
	are singletons, use range_true even if op1 != op2
	when one range is [-0.0, -0.0] and another [0.0, 0.0].  Similarly,
	even if intersection of the ranges is empty and one has
	zero low bound and another zero high bound, use range_true_and_false
	rather than range_false.
	(foperator_not_equal::fold_range): If both op1 and op2
	are singletons, use range_false even if op1 != op2
	when one range is [-0.0, -0.0] and another [0.0, 0.0].  Similarly,
	even if intersection of the ranges is empty and one has
	zero low bound and another zero high bound, use range_true_and_false
	rather than range_true.

	* gcc.c-torture/execute/ieee/pr108540-1.c: New test.
	* gcc.c-torture/execute/ieee/pr108540-2.c: New test.

1 files changed, 35 insertions, 5 deletions

diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 74ac465..2db83ae 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -607,6 +607,10 @@ foperator_equal::fold_range (irange &r, tree type,
     {
       if (op1 == op2)
 	r = range_true (type);
+      // If one operand is -0.0 and other 0.0, they are still equal.
+      else if (real_iszero (&op1.lower_bound ())
+	       && real_iszero (&op2.lower_bound ()))
+	r = range_true (type);
       else
 	r = range_false (type);
     }
@@ -617,7 +621,18 @@ foperator_equal::fold_range (irange &r, tree type,
       frange tmp = op1;
       tmp.intersect (op2);
       if (tmp.undefined_p ())
-	r = range_false (type);
+	{
+	  // If one range is [whatever, -0.0] and another
+	  // [0.0, whatever2], we don't know anything either,
+	  // because -0.0 == 0.0.
+	  if ((real_iszero (&op1.upper_bound ())
+	       && real_iszero (&op2.lower_bound ()))
+	      || (real_iszero (&op1.lower_bound ())
+		  && real_iszero (&op2.upper_bound ())))
+	    r = range_true_and_false (type);
+	  else
+	    r = range_false (type);
+	}
       else
 	r = range_true_and_false (type);
     }
@@ -708,10 +723,14 @@ foperator_not_equal::fold_range (irange &r, tree type,
   // consist of a single value, and then compare them.
   else if (op1.singleton_p () && op2.singleton_p ())
     {
-      if (op1 != op2)
-	r = range_true (type);
-      else
+      if (op1 == op2)
 	r = range_false (type);
+      // If one operand is -0.0 and other 0.0, they are still equal.
+      else if (real_iszero (&op1.lower_bound ())
+	       && real_iszero (&op2.lower_bound ()))
+	r = range_false (type);
+      else
+	r = range_true (type);
     }
   else if (!maybe_isnan (op1, op2))
     {
@@ -720,7 +739,18 @@ foperator_not_equal::fold_range (irange &r, tree type,
       frange tmp = op1;
       tmp.intersect (op2);
       if (tmp.undefined_p ())
-	r = range_true (type);
+	{
+	  // If one range is [whatever, -0.0] and another
+	  // [0.0, whatever2], we don't know anything either,
+	  // because -0.0 == 0.0.
+	  if ((real_iszero (&op1.upper_bound ())
+	       && real_iszero (&op2.lower_bound ()))
+	      || (real_iszero (&op1.lower_bound ())
+		  && real_iszero (&op2.upper_bound ())))
+	    r = range_true_and_false (type);
+	  else
+	    r = range_true (type);
+	}
       else
 	r = range_true_and_false (type);
     }