Actually, I'd say that support for fast range checks is less important in Rust than in some other languages, because the Rust compiler is quite good at removing the checks when a value can be proven to be in the right range. In general, Rust seems to cope quite well with current CPU architectures, although I do think that there's an open question as to how to support viable parallelism that not quite as fine-grained as current ILP approaches (pipelining, superscalar), nor quite as coarse as to be effectively exploited via multiple threads. ISTM that this is one portion of the design space that Rust might address quite nicely.