> By avoiding privileged optimizations in the frontend and by giving programmers low-level tools where they need them, Rust empowers library authors to get thin

> By avoiding privileged optimizations in the frontend and by giving programmers low-level tools where they need them, Rust empowers library authors to get things done without having to bug the Rust developers themselves to implement them. And there are cases where it is desirable to use unsafe indexing (beyond implementing the standard library iterators). While LLVM is able to get rid of nounds-checking for a simple indexing loop, it's less likely to do in other circumstances. For example, a high-performance sorting function might want to use (some) unsafe indexing. The access patterns and loop exit conditions can be very complex, and LLVM will not be clever enough to reliable optimize out bounds checks.