Reduced from gcc.c-torture/execute/builtins/string-asm-2*

typedef __SIZE_TYPE__ size_t;
extern void abort (void);
extern void bcopy (const void *, void *, size_t);

char y[64] = "foX";

void *
memcpy (void *d, const void *s, size_t n)
{
  char *dst = (char *) d;
  const char *src = (const char *) s;
  while (n--)
    *dst++ = *src++;
  return (char *) d;
}

int
main (void)
{
  bcopy (y + 1, y + 2, 3);
  if (y[3] != 'X')
    abort ();

  return 0;
}

With -O0, bcopy stays as is in the final assembly output.
With -O1 and above, bcopy is somehow transformed into memcpy.

This problem seems to occur at expand-time.

On mainline, this problem does not exist.