It is. As far as I know, rustc just exposes LLVM’s LTO functionality, without performing any Rust-specific optimizations at link time. So you get the same opt

It is. As far as I know, rustc just exposes LLVM’s LTO functionality, without performing any Rust-specific optimizations at link time. So you get the same optimizations as you would with LTO in Clang (C compiler), and indeed you can do cross-language LTO between the two. Also, even without LTO, LLVM can perform the same ABI optimizations on functions that are local to a single translation unit and not exported to other ones. In Rust that means a function not exported across crate boundaries. In C that means a `static` function.