Vector peeling cost model 3/6

gcc/ChangeLog:

2017-05-30  Robin Dapp  <rdapp@linux.vnet.ibm.com>

	* tree-vect-data-refs.c (vect_peeling_hash_choose_best_peeling):
	Return peeling info and set costs to zero for unlimited cost
	model.
	(vect_enhance_data_refs_alignment): Also inspect all datarefs
	with unknown misalignment. Compute and costs for unknown
	misalignment, compare them to the costs for known misalignment
	and choose the cheapest for peeling.

From-SVN: r248677