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We'd like that too; it's likely to fall out of const generics, which are looking likely to hit stable sometime early next year.

With const generics ranged integers would be implemented as a user specified check.

How viable would it be to implement an optimization step which seeks to minimize the number of these checks?

I'm not entirely sure what you mean, exactly. As far as I know, all of the usual optimization passes would already be working to minimize them.

Rust could emit LLVM range metadata for ranged integers. IIRC, it already does so for enum discriminants.

That seems quite good!