With -D_FORTIFY_SOURCE=2 memmove is folded to memcpy because of the restrict
qualified arguments of the memmove wrapper.

"Miscompiled" at -O1:

typedef __SIZE_TYPE__ size_t;
extern void *memmove (void *__dest, __const void *__src, size_t __n)
     __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));

extern __inline __attribute__ ((__always_inline__)) __attribute__ ((__artificial__)) void *
__attribute__ ((__nothrow__)) memmove (void *__restrict __dest, __const void *__restrict __src, size_t __len)

{
  return __builtin___memmove_chk (__dest, __src, __len, __builtin_object_size (__dest, 0));
}
extern void abort (void);
void __attribute__((noinline,noclone))
foo(void *p, void *q)
{
  memmove (p, q, 13);
}
int main()
{
  char a[32] = "Hello World!";
  foo (&a[1], a);
  if (strcmp (a, "HHello World!") != 0)
    abort ();
  foo (a, &a[1]);
  if (strcmp (a, "Hello World!") != 0)
    abort ();
  return 0;
}

But IMHO this is a serious glibc bug.