Handle polynomial DR_INIT

Handle polynomial DR_INIT

The idea with the main 107-patch poly_int series (latterly 109-patch)
was to change the mode sizes and vector element counts to poly_int and
then propagate those changes as far as they needed to go to fix build
failures from incompatible types.  This means that DR_INIT is now
constructed as a poly_int64:

  poly_int64 pbytepos;
  if (!multiple_p (pbitpos, BITS_PER_UNIT, &pbytepos))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file, "failed: bit offset alignment.\n");
      return false;
    }
  [...]
  init = ssize_int (pbytepos);

This patch adjusts other references to DR_INIT accordingly.  Unlike
the above, the adjustments weren't needed to avoid a build-time type
incompatibility, but they are needed to make the producer and consumers
of DR_INIT logically consistent.

2018-01-12  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-predcom.c (aff_combination_dr_offset): Use wi::to_poly_widest
	rather than wi::to_widest for DR_INITs.
	* tree-vect-data-refs.c (vect_find_same_alignment_drs): Use
	wi::to_poly_offset rather than wi::to_offset for DR_INIT.
	(vect_analyze_data_ref_accesses): Require both DR_INITs to be
	INTEGER_CSTs.
	(vect_analyze_group_access_1): Note that here.

From-SVN: r256587