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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/101610] New: CST - (x ^ (CST-1)) can be
 optimized to x + 1 if x < CST and CST is a power of 2
Date: Sat, 24 Jul 2021 06:20:15 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101610

            Bug ID: 101610
           Summary: CST - (x ^ (CST-1)) can be optimized to x + 1 if x <
                    CST and CST is a power of 2
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
unsigned long f(unsigned long x)
{
    if (x >=3D 64)__builtin_unreachable();
    x =3D x ^ 63;
unsigned long y =3D (unsigned long )x;
unsigned long z =3D 64 - y;
return z;
}
This should just be:
unsigned long long f1(unsigned long x)
{
  return x + 1;
}=