PR tree-opt/18536
        * tree-vectorizer.c (make_loop_iterate_ntimes): Use type of niters when
        creating iv instead of integer_type.
        (vect_build_loop_niters): Remove redundant code.
        (vect_transform_loop_bound): Removed (duplicates functionality of
        make_loop_iterate_ntimes.
        (vect_gen_niters_for_prolog_loop): Add documentation. Call
        lang_hooks.types.type_for_size to create a type of the required size.
        Use that type instead of integer_type. Remove redundant code.
        (vect_update_niters_after_peeling): Use type of niters instead of
        integer_type.
        (vect_transform_loop): Unify handling of known and unknown loop bound
        cases. Call make_loop_iterate_ntimes instead of
        vect_transform_loop_bound.

From-SVN: r91014