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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/99101] optimization bug with -ffinite-loops
Date: Thu, 25 Feb 2021 12:09:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99101

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
Further simplified, but still depends on -ffinite-loops

volatile int xx;
int main()
{
  int jobs_ =3D 1;
  int at_eof_ =3D 0;
  while (1)
    {
      for (int i =3D 0; i < jobs_; i++)
        {
          if (at_eof_)
            continue;
          at_eof_ =3D 1;
          __builtin_printf ("1\n");
          if (xx)
            return 1;
        }
      jobs_ =3D 0;
    }
  return 0;
}

if one exchanges the at_eof_ test with a function call like if (at_eof ()) =
then
the side-effect of at_eof() marks the if necessary by means of the block
being control dependent on itself.=