[Bug tree-optimization/58715] Missed loop condition optimization opportunity

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58715

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Here is a testcase which shows we are not doing some other loop opt due to not
changing the loop:
typedef __SIZE_TYPE__ size_t;

void f(int mlen, unsigned char *dst, size_t d_len, unsigned char *cpy)
{
  unsigned char *d_end = dst + d_len;

  while (--mlen >= 0 && dst < d_end)
    *dst++ = 0;
}

This should produce memset but we are not currently.