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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/96681] New: Failure to optimize xor of
 comparisons with specific constants to comparison of xor-ed of compared
 variables
Date: Tue, 18 Aug 2020 16:36:53 +0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 11.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96681

            Bug ID: 96681
           Summary: Failure to optimize xor of comparisons with specific
                    constants to comparison of xor-ed of compared
                    variables
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f(int x, int y)
{
    return (x < 0) ^ (y < 0);
}

This can be optimized to `return (x ^ y) < 0;`. LLVM does this transformati=
on,
but GCC does not. This transformation can also be done with `return (x > -1=
) ^
(y > -1);`. There is also a similar transformation with `return (x > -1) ^ =
(y <
0);`, which can be optimized to `return ~(x ^ y) < 0;`.=