In reply to UVM_LOVE:
When calling ‘add_hdl_path_slice’, you need to provide the name of the RTL register. The three fields that you are defining are in the RTL register ‘control_reg’
//To access BACKDOOR
add_hdl_path_slice( .name("control_reg"), .offset(2), .size(1));
add_hdl_path_slice( .name("control_reg"), .offset(1), .size(1));
add_hdl_path_slice( .name("control_reg"), .offset(0), .size(1));