path solver: Use ranger to solve unknowns.

path solver: Use ranger to solve unknowns.

The default behavior for the path solver is to resort to VARYING when
the range for an unknown SSA is outside the given path.  This is both
cheap and fast, but fails to get a significant amount of ranges that
traditionally the DOM and VRP threaders could get.

This patch uses the ranger to resolve any unknown names upon entry to
the path.  It also uses equivalences to improve ranges.

gcc/ChangeLog:

	* gimple-range-path.cc (path_range_query::defined_outside_path):
	New.
	(path_range_query::range_on_path_entry): New.
	(path_range_query::internal_range_of_expr): Resolve unknowns
	with ranger.
	(path_range_query::improve_range_with_equivs): New.
	(path_range_query::ssa_range_in_phi): Resolve unknowns with
	ranger.
	* gimple-range-path.h (class path_range_query): Add
	defined_outside_path, range_on_path_entry, and
	improve_range_with_equivs.