Added an as-yet-unused hash function for exprs
Added an as-yet-unused hash function for exprs


Former-commit-id: 7151c3b3e8f282b6209b2d9e18306fc6b5f0f890
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide