Vector peeling cost model 4/6

Vector peeling cost model 4/6

gcc/ChangeLog:

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

	* tree-vect-data-refs.c (vect_get_data_access_cost):
	Workaround for SLP handling.
	(vect_enhance_data_refs_alignment):
	Compute costs for doing no peeling at all, compare to the best
	peeling costs so far and avoid peeling if cheaper.

From-SVN: r248678