combine.c (reg_subword_p): New predicate to test whether the destination of a set refers to a...

	* combine.c (reg_subword_p): New predicate to test whether the
	destination of a set refers to a subword/piece of a register.
	(try_combine): Generalize the code to merge the setting of a
	pseudo to a constant followed by a set of a subword of that
	register to a constant.

From-SVN: r109267