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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/94796] New: Failure to reuse flags from
 substraction
Date: Mon, 27 Apr 2020 12:32:50 +0000
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X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 10.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94796

            Bug ID: 94796
           Summary: Failure to reuse flags from substraction
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f(int a, int b)
{
    return ((a =3D=3D b) & (a - b));
}

The `a =3D=3D b` is able to use condition flags resulting from `a - b`, and=
 thus
avoid an extra compare. LLVM does this transformation, but GCC does not.

https://godbolt.org/z/SHvTW8=