* gcse.c (struct bb_data): Add new fields, old_pressure, live_in
	and backup.
	(get_regno_pressure_class): Add prototype.
	(update_bb_reg_pressure): New.
	(should_hoist_expr_to_dom): Add new parameter from.
	Monitor the change of reg pressure and use it to drive hoisting.
	(hoist_code): Update LIVE and reg pressure information.
	(calculate_bb_reg_pressure): Initialize live_in and backup.

	* gcc.dg/hoist-register-pressure-3.c: New test.

From-SVN: r193425