lower-subreg.c (find_decomposable_subregs): Turn from being a for_each_rtx callback to being a function that examines each...

gcc/
	* lower-subreg.c (find_decomposable_subregs): Turn from being
	a for_each_rtx callback to being a function that examines each
	subrtx itself.  Remove handling of null rtxes.
	(decompose_multiword_subregs): Update accordingly.

From-SVN: r214649