Add a vect_get_scalar_dr_size helper function

Add a vect_get_scalar_dr_size helper function

This patch adds a helper function for getting the number of bytes
accessed by an unvectorised data reference, which helps when general
modes have a variable size.

2017-09-22  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-vectorizer.h (vect_get_scalar_dr_size): New function.
	* tree-vect-data-refs.c (vect_update_misalignment_for_peel): Use it.
	(vect_enhance_data_refs_alignment): Likewise.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r253099