Large memcpy

We are using Keil C-51 V7.06.

There is a structure defined:

typedef struct
{
  unsigned char address_bus_h;
  unsigned char address_bus_l;
  unsigned char data_bus;
}instbus_raw_t;

Using three simple lines to copy the structure to another it enlarges code by 9 bytes, but this is not an elegant solution:

instbus_raw.address_bus_h = instbus_raw_local.address_bus_h;
instbus_raw.address_bus_l = instbus_raw_local.address_bus_l;
instbus_raw.data_bus = instbus_raw_local.data_bus;

Using the normal library function memcpy
blows up the code by 300 bytes!

memcpy(&instbus_raw,&instbus_raw_local,sizeof(instbus_raw_t));

Using an own function my_memcpy the code increases by 167 bytes:

void *(my_memcpy)(void *s1, const void *s2, size_t n)
{
  char *su1 = (char *)s1;
  const char *su2 = (const char *)s2;

  for (; 0 < n; --n)
    *su1++ = *su2++;
  return (s1);
}

my_memcpy(&instbus_raw,&instbus_raw_local,sizeof(struct instbus_raw_t));

In a project with a little chip of 2k Flash, 300 bytes for copying few bytes are considerable!

Does anyone remarking same effects with library functions wasting resources?

Regards Peter