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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/57832] compiling sha-256 code (xz 5.0.5) generates
 false warnings when using -march=native on Atom CPU
Date: Sun, 28 Mar 2021 11:17:40 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D57832

--- Comment #7 from Manuel L=C3=B3pez-Ib=C3=A1=C3=B1ez <manu at gcc dot gnu=
.org> ---
(In reply to Martin Sebor from comment #6)
> In the reduced test cases (in comment #3 and comment #4) d is a global
> variable so it's value is zero.  c is assigned in the first iteration of =
the
> loop (when e is zero) and used in subsequent iterations when it has a
> defined value, so the warning .seems like a clear false postive to me.  (I
> didn't look at the big test case.)

Oh, yes! Sorry, my comment didn't make sense. Even simpler:

int a, d;

void f (void)
{
  int c;
  for (int e =3D 0; e < 64; e +=3D 6)
    {
      if (e =3D=3D 0)
            c =3D d;
      else=20
            a +=3D c;
    }
}=