Use non-null knowledge in path_range_query.

Use non-null knowledge in path_range_query.

This patch improves ranges for pointers we are interested in a path, by
using the non-null class from the ranger.  This allows us to thread more
paths with minimal effort.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* gimple-range-path.cc (path_range_query::range_defined_in_block):
	Adjust for non-null.
	(path_range_query::adjust_for_non_null_uses): New.
	(path_range_query::precompute_ranges): Call
	adjust_for_non_null_uses.
	* gimple-range-path.h: Add m_non_null and
	adjust_for_non_null_uses.