function live in info

Hi
   I find various argument lowering functions that add registers to
function live in do the following

   args_float[ArgNo] = AddLiveIn(MF, args_float[ArgNo],
                                      &Alpha::F4RCRegClass);

   Do these live in registers get used later during liveness
analysis/register allocation ? How can I verify if it has indeed
impacted the live intervals?

thanks
shrey