path solver: Add relation support.

path solver: Add relation support.

This patch adds relational support to the path solver.  It uses a
path_oracle that keeps track of relations within a path which are
augmented by relations on entry to the path.  With it, range_of_stmt,
range_of_expr, and friends can give relation aware answers.

gcc/ChangeLog:

	* gimple-range-fold.h (class fur_source): Make oracle protected.
	* gimple-range-path.cc (path_range_query::path_range_query): Add
	resolve argument.  Initialize oracle.
	(path_range_query::~path_range_query): Delete oracle.
	(path_range_query::range_of_stmt): Adapt to use relations.
	(path_range_query::precompute_ranges): Pre-compute relations.
	(class jt_fur_source): New
	(jt_fur_source::jt_fur_source): New.
	(jt_fur_source::register_relation): New.
	(jt_fur_source::query_relation): New.
	(path_range_query::precompute_relations): New.
	(path_range_query::precompute_phi_relations): New.
	* gimple-range-path.h (path_range_query): Add resolve argument.
	Add oracle, precompute_relations, precompute_phi_relations.
	* tree-ssa-threadbackward.c (back_threader::back_threader): Pass
	resolve argument to solver.