[Bug tree-optimization/71428] [7 Regression] wrong code with -Os -fno-tree-forwprop (breaks in the .bswap dump)

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71428

--- Comment #2 from Zdenek Sojka <zsojka at seznam dot cz> ---
I cannot upload any attachment to bugzilla (requests just time out), so here it
is as a plain text:
$ cat testcase.c
typedef unsigned short v64u16 __attribute__ ((vector_size (64)));

v64u16
foo (v64u16 p1)
{
  p1[31] |= p1[1];
  return p1;
}

int
main ()
{
  v64u16 x = foo ((v64u16){ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 });
//  __builtin_printf ("%04x\n", x[31]);
  if (x[31] != 1)
    __builtin_abort();
  return 0;
}