bool get_op(Op *op)
{
  static UINT64 unique_count = 1;
  Trace_op trace_op;
  bool success = FALSE;
  // read trace 
  // fill out op info 
  // return FALSE if the end of trace
  int read_size;
  read_size = gzread(g_stream, &trace_op, sizeof(Trace_op));
  success = read_size>0;

  if(read_size!=sizeof(Trace_op) && read_size>0) 
    success = false;

  if (KNOB(KNOB_PRINT_INST)->getValue()) dprint_trace(&trace_op);

  /* copy trace structure to op */
  if (success) {
    copy_trace_op(&trace_op, op);

    op->inst_id  = unique_count++;
    op->valid    = TRUE;
  }
  return success;
}