[PATCH] range-ops: (nonzero | X) is nonzero

[Bernhard Reutner-Fischer]

On 15 June 2021 13:48:39 CEST, Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>For bitwise or, nonzero|X is always nonzero.  Make sure we don't drop
>to
>varying in this case.
>
>This was found while examining differences between VRP/DOM threaders
>and
>the upcoming work, but it could be useful for any user of range-ops.
>
>Tested on x86-64 Linux.
>
>OK?
>
>gcc/ChangeLog:
>
>	* range-op.cc (operator_bitwise_or::wi_fold): Make sure
>	nonzero|X is nonzero.
>	(range_op_bitwise_and_tests): Add tests for above.
>---
> gcc/range-op.cc | 28 ++++++++++++++++++++++++----
> 1 file changed, 24 insertions(+), 4 deletions(-)
>
>diff --git a/gcc/range-op.cc b/gcc/range-op.cc
>index 742e54686b4..59978466b45 100644
>--- a/gcc/range-op.cc
>+++ b/gcc/range-op.cc
>@@ -2534,11 +2534,20 @@ operator_bitwise_or::wi_fold (irange &r, tree
>type,
>     new_lb = wi::max (new_lb, lh_lb, sign);
>   if (wi::lt_p (rh_ub, 0, sign))
>     new_lb = wi::max (new_lb, rh_lb, sign);
>-  // If the limits got swapped around, return varying.
>+  // If the limits got swapped around, return a conservative range.
>   if (wi::gt_p (new_lb, new_ub,sign))

Missing space before sign above?

>-    r.set_varying (type);
>-  else
>-    value_range_with_overflow (r, type, new_lb, new_ub);
>+    {
>+      // Make sure that nonzero|X is nonzero.
>+      if (wi::gt_p (lh_lb, 0, sign)
>+	  || wi::gt_p (rh_lb, 0, sign)
>+	  || wi::lt_p (lh_ub, 0, sign)
>+	  || wi::lt_p (rh_ub, 0, sign))
>+	r.set_nonzero (type);
>+      else
>+	r.set_varying (type);
>+      return;
>+    }
>+  value_range_with_overflow (r, type, new_lb, new_ub);
> }
> 
> bool
>@@ -3744,6 +3753,17 @@ range_op_bitwise_and_tests ()
>   i1 = int_range<1> (integer_type_node);
>   op_bitwise_and.op1_range (res, integer_type_node, i1, i2);
>   ASSERT_TRUE (res == int_range<1> (integer_type_node));
>+
>+  // (NONZERO | X) is nonzero.
>+  i1.set_nonzero (integer_type_node);
>+  i2.set_varying (integer_type_node);
>+  op_bitwise_or.fold_range (res, integer_type_node, i1, i2);
>+  ASSERT_TRUE (res.nonzero_p ());
>+
>+  // (NEGATIVE | X) is nonzero.
>+  i1 = int_range<1> (INT (-5), INT (-3));
>+  i2.set_varying (integer_type_node);
>+  op_bitwise_or.fold_range (res, integer_type_node, i1, i2);

Wouldn't you want to assert something here?
thanks,
> }
> 
> void