rtx structure

["Bharati Bhole" <bharati.bhole@xxxxxxxxx>]

I am not able to understand the structure of rtx_def fully its too complicated.
Could anybody please guide me. Its defined in rtl.h.
struct rtx_def GTY((chain_next ("RTX_NEXT (&%h)"),
                   chain_prev ("RTX_PREV (&%h)")))
{
  ENUM_BITFIELD(rtx_code) code: 16;
 ENUM_BITFIELD(machine_mode) mode : 8;
 unsigned int jump : 1;
 unsigned int call : 1;
 unsigned int unchanging : 1;
 unsigned int volatil : 1;
 unsigned int in_struct : 1;
  unsigned int used : 1;
 unsigned frame_related : 1;
 unsigned return_val : 1;
 union u {
   rtunion fld[1];
   HOST_WIDE_INT hwint[1];
 } GTY ((special ("rtx_def"), desc ("GET_CODE (&%0)"))) u;
};

Thanks,
Bharati.