tree-vect-data-refs.c (vect_preserves_scalar_order_p): Make sure to use non-pattern stmts for get_earlier_stmt arguments.

2018-05-29  Richard Biener  <rguenther@suse.de>

	* tree-vect-data-refs.c (vect_preserves_scalar_order_p): Make
	sure to use non-pattern stmts for get_earlier_stmt arguments.
	* tree-vectorizer.h (get_earlier_stmt): Assert we do not get
	called on pattern stmts.
	(get_later_stmt): Likewise.

From-SVN: r260896