[PeCaN]

Ada and Rust are both significantly easier to perform aliasing analysis on, so frequently you can get much better code. Both languages have slight overhead for bounds checking and such, but you can turn it off (at least in Ada) if it's a problem (hint: it isn't).

Same reason Fortran is fast actually: it just disallows pointer aliasing entirely¹, meaning you get none of the flexibility of C pointers (heck, you don't even have pointers, basically), but if you're multiplying matrices it flies.

¹ I recall newer Fortrans have pointers, but as I'm not a Fortran programmer I don't actually know.

[steveklabnik]

You can call get_unchecked() instead of [] to elide the bounds checking at any place that does it in Rust.