range-op-float: Only flush_denormals_to_zero for +-*/ [PR109154]

As discussed in the PR, flushing denormals to zero on every frange::set
might be harmful for e.g. x < 0.0 comparisons, because we then on both
sides use ranges that include zero [-Inf, -0.0] on the true side, and
[-0.0, +Inf] NAN on the false side, rather than [-Inf, nextafter (-0.0, -Inf)]
on the true side.

The following patch does it only in range_operator_float::fold_range
which is right now used for +-*/ (both normal and reverse ops of those).

Though, I don't see any difference on the testcase in the PR, but not sure
what I should be looking at and the reduced testcase there has undefined
behavior.

2023-03-28  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/109154
	* value-range.h (frange::flush_denormals_to_zero): Make it public
	rather than private.
	* value-range.cc (frange::set): Don't call flush_denormals_to_zero
	here.
	* range-op-float.cc (range_operator_float::fold_range): Call
	flush_denormals_to_zero.

diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index dc9789b..d212e64 100644 (file)
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -112,6 +112,8 @@ range_operator_float::fold_range (frange &r, tree type,
        }
     }
 
+  r.flush_denormals_to_zero ();
+
   return true;
 }
 

diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index ec97e76..ec826c2 100644 (file)
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -361,8 +361,6 @@ frange::set (tree type,
 
   normalize_kind ();
 
-  flush_denormals_to_zero ();
-
   if (flag_checking)
     verify_range ();
 }

diff --git a/gcc/value-range.h b/gcc/value-range.h
index 2b4f6e9..969b2b6 100644 (file)
--- a/gcc/value-range.h
+++ b/gcc/value-range.h
@@ -373,6 +373,7 @@ public:
   void update_nan (tree) = delete; // Disallow silent conversion to bool.
   void update_nan (const nan_state &);
   void clear_nan ();
+  void flush_denormals_to_zero ();
 
   // fpclassify like API
   bool known_isfinite () const;
@@ -389,7 +390,6 @@ private:
   bool union_nans (const frange &);
   bool intersect_nans (const frange &);
   bool combine_zeros (const frange &, bool union_p);
-  void flush_denormals_to_zero ();
 
   tree m_type;
   REAL_VALUE_TYPE m_min;