Make range_from_dom more effective.

Make range_from_dom more effective.

Add modes to range_from_dom such that we can simply query, or adjust the
cache and deal with multiple predecessor blocks.

	* gimple-range-cache.cc (ranger_cache::ranger_cache): Start with
	worlist truncated.
	(ranger_cache::entry_range): Add rfd_mode parameter.
	(ranger_cache::exit_range): Ditto.
	(ranger_cache::edge_range): New.  Incorporate from range_on_edge.
	(ranger_cache::range_of_expr): Adjust call to entry_range.
	(ranger_cache::range_on_edge): Split to edge_range and call.
	(ranger_cache::fill_block_cache): Always invoke range_from_dom.
	(ranger_cache::range_from_dom): Make reentrant, add search mode, handle
	mutiple predecessors.
	(ranger_cache::update_to_nonnull): Adjust call to exit_range.
	* gimple-range-cache.h (ranger_cache): Add enum rfd_mode.  Adjust
	prototypes.