lower-subreg.c (shift_cost): Use set_src_cost, avoiding the SET.

lower-subreg.c (shift_cost): Use set_src_cost, avoiding the SET.

gcc/
	* lower-subreg.c (shift_cost): Use set_src_cost, avoiding the SET.
	(compute_costs): Likewise for the zero extension.  Use set_rtx_cost
	to compute the cost of moves.  Set the mode of the target register.

From-SVN: r187212