* loop.h (express_from): Declare.
	(struct induction): Replace derived flag with derived_from pointer.
	* loop.c (strength_reduce, record_giv, recombine_givs): Likewise.
	(express_from): No longer static.
	* unroll.c (find_splittable_givs): Replace derived with derived_from.
	When processing an address giv with which another giv has been
	combined that has also been derived from a third giv, handle like
	having combined with the third giv.
	Set splittable_regs_updates appropriately for derived givs.

From-SVN: r25007