> At this time there is no portable way to produce computed gotos or tail call optimization in compiled machine code from Rust.

Nightly rust now has the `become` keyword:

https://doc.rust-lang.org/std/keyword.become.html

> `feature(explicit_tail_calls)` is currently incomplete and may not work properly.

Works on my machine (tm). At least with toy examples. Including in full optimizationless debug mode, turning `call`s into `jmp`s ensuring `factorial(usize::MAX)` won't stack overflow probably maybe.

https://rust.godbolt.org/z/7xf836E8K

> checked_sub? wrapping_mul? MaulingMonkey, what's wrong with you?

Eliminating debug-mode panic boilerplate.