poly_int: fold_indirect_ref_1

poly_int: fold_indirect_ref_1

This patch makes fold_indirect_ref_1 handle polynomial offsets in
a POINTER_PLUS_EXPR.  The specific reason for doing this now is
to handle:

 		  (tree_to_uhwi (part_width) / BITS_PER_UNIT
 		   * TYPE_VECTOR_SUBPARTS (op00type));

when TYPE_VECTOR_SUBPARTS becomes a poly_int.

2018-01-03  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* fold-const.c (fold_indirect_ref_1): Handle polynomial offsets
	in a POINTER_PLUS_EXPR.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r256146