This patch makes get_inner_reference_aff return the size as a
poly_widest_int rather than a widest_int.

2017-12-20  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-affine.h (get_inner_reference_aff): Return the size as a
	poly_widest_int.
	* tree-affine.c (get_inner_reference_aff): Likewise.
	* tree-data-ref.c (dr_may_alias_p): Update accordingly.
	* tree-ssa-loop-im.c (mem_refs_may_alias_p): Likewise.

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

From-SVN: r255891