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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/108657] [13 Regression] csmith: possible wrong
 checksum with -O3 and -ftrivial-auto-var-init=zero
Date: Wed, 15 Feb 2023 18:22:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108657

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Slightly cleaned up; aborts with -O3 -ftrivial-auto-var-init=3Dzero,
doesn't abort with -O0, -O3 or -O0 -ftrivial-auto-var-init=3Dzero.

int m[256];
unsigned n =3D 4294967295;

void
foo (int b)
{
  n =3D (n >> 8) ^ m[(n ^ b) & 255];
}

void
bar (long x)
{
  n =3D (n >> 8) ^ m[(n ^ x) & 255];
  foo (x >> 8);
  foo (x >> 16);
  foo (x >> 24);
  foo (x >> 32);
  foo (x >> 40);
  foo (x >> 48);
  foo (x >> 56);
}

int a =3D -8, c, e, f, g, i;
short b;
static int *d =3D &c;
unsigned h;

int
main ()
{
  if (__CHAR_BIT__ !=3D 8 || __SIZEOF_SHORT__ !=3D 2 || __SIZEOF_INT__ !=3D=
 4)
    return 0;
  for (; g < 256; g++)
    {
      h =3D g;
      for (i =3D 8; i; i--)
        if (h & 1)
          h =3D (h >> 1) ^ 3988292384;
        else
          h >>=3D 1;
      m[g] =3D h;
    }
  b =3D 53935 & a;
  a =3D -18;
  for (c =3D 1; c >=3D 0; c -=3D 1)
    {
      e =3D 0;
      for (int j =3D 0; j <=3D 3; j++)
        {
          short k[1];
          if (e)
            break;
          e ^=3D f;
        }
    }
  *d =3D 8 || 0;
  bar (a);
  bar (b);
  bar (2185655400);
  bar (c);
  if (n !=3D 0xbd51857cU)
    __builtin_abort ();
}

The only difference between -O3 and -O3 -ftrivial-auto-var-init=3Dzero in g=
imple
dump
is the addition of
            k =3D .DEFERRED_INIT (2, 2, &"k"[0]);
where k is otherwise unused variable.=