Well, there is mrustc[0], a Rust compiler that doesn't include a borrow-checker, so it's possible to compile (at least some versions of) Rust without a borrow c

Well, there is mrustc[0], a Rust compiler that doesn't include a borrow-checker, so it's possible to compile (at least some versions of) Rust without a borrow checker, though it might not result in the most optimized code. AFAIK there are some optimization like the infamous `noalias` optimization (which took several tries to get turned on[1]) that uses information established during borrow checking. I'm also not sure what the relation with NLL (non-lexical lifetimes) is, where I would assume you would need at least a primitive borrow-checker to establish some information that the backend might be interested in. Then again, mrustc compiles Rust versions that have NLL features without a borrow-checker, so it's again probably more on the optimization side than being essential. [0]: https://github.com/thepowersgang/mrustc https://github.com/thepowersgang/mrustc [1]: https://stackoverflow.com/a/57259339 https://stackoverflow.com/a/57259339