With Debian's gcc-snapshot 20150722-1 on the following program, I get an incorrect warning "array subscript is above array bounds".

unsigned char buffer[8];
unsigned long foo (void)
{
  unsigned long i;
  i = buffer[0];
  if (i >= 8)
    return i - 7;
  i++;
  while (i > 8)
    {
      if (buffer[i-1] != 0)
        return 0;
      i--;
    }
  return 1;
}

zira:~> gcc-snapshot -Wall -O2 -c tst.c
tst.c: In function 'foo':
tst.c:11:17: warning: array subscript is above array bounds [-Warray-bounds]
       if (buffer[i-1] != 0)
                 ^

I don't get this warning if I use -O1 or gcc-snapshot 20150701-1 (thus this problem is very recent) or GCC 5.1.1 (gcc-5 Debian package).

Notes:
* There are other bugs concerning this warning, but they are older, while here this is a recent regression.
* The above code has been obtained by simplifying MPFR's mpfr_fpif_read_precision_from_file function in fpif.c (trunk).