This patch changes C++ bitregion_start/end values from constants to
poly_ints.  Although it's unlikely that the size needs to be polynomial
in practice, the offset could be with future language extensions.

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

gcc/
	* expmed.h (store_bit_field): Change bitregion_start and
	bitregion_end from unsigned HOST_WIDE_INT to poly_uint64.
	* expmed.c (adjust_bit_field_mem_for_reg, strict_volatile_bitfield_p)
	(store_bit_field_1, store_integral_bit_field, store_bit_field)
	(store_fixed_bit_field, store_split_bit_field): Likewise.
	* expr.c (store_constructor_field, store_field): Likewise.
	(optimize_bitfield_assignment_op): Likewise.  Make the same change
	to bitsize and bitpos.
	* machmode.h (bit_field_mode_iterator): Change m_bitregion_start
	and m_bitregion_end from HOST_WIDE_INT to poly_int64.  Make the
	same change in the constructor arguments.
	(get_best_mode): Change bitregion_start and bitregion_end from
	unsigned HOST_WIDE_INT to poly_uint64.
	* stor-layout.c (bit_field_mode_iterator::bit_field_mode_iterator):
	Change bitregion_start and bitregion_end from HOST_WIDE_INT to
	poly_int64.
	(bit_field_mode_iterator::next_mode): Update for new types
	of m_bitregion_start and m_bitregion_end.
	(get_best_mode): Change bitregion_start and bitregion_end from
	unsigned HOST_WIDE_INT to poly_uint64.

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

From-SVN: r255879