* loop.c (strength_reduce): Call check_ext_dependant_givs.
Properly extend the biv initial value for the giv.
(record_biv): Zero ext_dependant.
(record_giv): New argument ext_val. Update all callers.
(general_induction_var): Likewise.
(consec_sets_giv): Likewise.
(simplify_giv_expr): Likewise. Fill in ext_val if we find
a sign-extend, zero-extend, or truncate.
(combine_givs_p): Make sure modes are compatible.
(check_ext_dependant_givs): New.
(extend_value_for_giv): New.
* loop.h (struct induction): Add ext_dependant.
* unroll.c (iteration_info): Extend the biv initial value for the giv.
(find_splittable_givs): Likewise.
(final_giv_value): Likewise.