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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110010] New: (a>>N) != (b>>N) is not
 optimized to (a^b) >= (1<<N)
Date: Sun, 28 May 2023 00:31:46 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110010

            Bug ID: 110010
           Summary: (a>>N) !=3D (b>>N) is not optimized to (a^b) >=3D (1<<N)
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
#define N 5
unsigned f(unsigned a, unsigned b)
{
  return (a>>N) !=3D (b>>N);
}
```
This could be optimized down to just `return (a^b) <=3D (1<<N)`.

This shows up in the testsuite as a pr94718-5.c failure when you add the
following 2 match patterns:
(simplify
 (negate (convert (lt @0 integer_zerop)))
 (if (!TYPE_UNSIGNED (TREE_TYPE (@0)))
  (with { tree type_unsigned =3D unsigned_type_for (TREE_TYPE (@0)); }
   (if (types_match (type, TREE_TYPE (@0)) || types_match (type_unsigned,
type))
    (convert (rshift @0
                     { build_int_cst (integer_type_node,
                                      element_precision (type) - 1); }))))))
(simplify
 (convert (lt @0 integer_zerop))
 (if (!TYPE_UNSIGNED (TREE_TYPE (@0)))
  (with { tree type_unsigned =3D unsigned_type_for (TREE_TYPE (@0)); }
   (if (types_match (type, TREE_TYPE (@0)) || types_match (type_unsigned,
type))
   (convert (rshift (convert:type_unsigned @0)
                    { build_int_cst (integer_type_node,
                                     element_precision (type) - 1); }))))))=