* gfortran.h (walk_code_fn_t, walk_expr_fn_t): New types.
	(gfc_expr_walker, gfc_code_walker): New prototypes.
	* frontend-passes.c (gfc_expr_walker, gfc_code_walker): New functions.
	(WALK_SUBEXPR, WALK_SUBEXPR_TAIL, WALK_SUBCODE): Define.
	(optimize_namespace): Use gfc_code_walker.
	(optimize_code, optimize_expr): Rewritten as gfc_code_walker hooks.
	(optimize_expr_0, optimize_code_node,
	optimize_actual_arglist): Removed.
	(optimize_assignment): Don't call optimize_expr_0.

From-SVN: r164342