Convert nonzero mask in irange to wide_int.

Convert nonzero mask in irange to wide_int.

The reason the nonzero mask was kept in a tree was basically inertia,
as everything in irange is a tree.  However, there's no need to keep
it in a tree, as the conversions to and from wide ints are very
annoying.  That, plus special casing NULL masks to be -1 is prone
to error.

I have not only rewritten all the uses to assume a wide int, but
have corrected a few places where we weren't propagating the masks, or
rather pessimizing them to -1.  This will become more important in
upcoming patches where we make better use of the masks.

Performance testing shows a trivial improvement in VRP, as things like
irange::contains_p() are tied to a tree.  Ughh, can't wait for trees in
iranges to go away.

gcc/ChangeLog:

	* value-range-storage.cc (irange_storage_slot::set_irange): Remove
	special case.
	* value-range.cc (irange::irange_set): Adjust for nonzero mask
	being a wide int.
	(irange::irange_set_anti_range): Same.
	(irange::set): Same.
	(irange::verify_range): Same.
	(irange::legacy_equal_p): Same.
	(irange::operator==): Same.
	(irange::contains_p): Same.
	(irange::legacy_intersect): Same.
	(irange::legacy_union): Same.
	(irange::irange_single_pair_union): Call union_nonzero_bits.
	(irange::irange_union): Same.
	(irange::irange_intersect): Call intersect_nonzero_bits.
	(irange::intersect): Adjust for nonzero mask being a wide int.
	(irange::invert): Same.
	(irange::set_nonzero_bits): Same.
	(irange::get_nonzero_bits_from_range): New.
	(irange::set_range_from_nonzero_bits): New.
	(irange::get_nonzero_bits): Adjust for nonzero mask being a wide
	int.
	(irange::intersect_nonzero_bits): Same.
	(irange::union_nonzero_bits): Same.
	(range_tests_nonzero_bits): Remove test.
	* value-range.h (irange::varying_compatible_p): Adjust for nonzero
	mask being a wide int.
	(gt_ggc_mx): Same.
	(gt_pch_nx): Same.
	(irange::set_undefined): Same.
	(irange::set_varying): Same.
	(irange::normalize_kind): Same.