path solver: Prefer range_of_expr instead of range_on_edge.

path solver: Prefer range_of_expr instead of range_on_edge.

The range_of_expr method provides better caching than range_on_edge.
If we have a statement, we can just it and avoid the range_on_edge
dance.  Plus we can use all the range_of_expr fanciness.

Tested on x86-64 and ppc64le Linux with the usual regstrap.  I also
verified that the before and after number of threads was the same or
greater in a suite of .ii files from a bootstrap.

gcc/ChangeLog:

	PR tree-optimization/102943
	* gimple-range-path.cc (path_range_query::range_on_path_entry):
	Prefer range_of_expr unless there are no statements in the BB.