tree-dfa.c (get_ref_base_and_extent): Do the offset computation using the precision of the index type.

	* tree-dfa.c (get_ref_base_and_extent) <ARRAY_REF>: Do the offset
	computation using the precision of the index type.
	* gimple-fold.c (fold_const_aggregate_ref_1) <ARRAY_REF>: Likewise.
	(fold_array_ctor_reference): Do index computations in the index type.

From-SVN: r187268