The performance ceiling of C++ is substantially lower than that of Rust. For example, it is roughly impossible for humans to use `restrict` with C or C++, while it's a completely normal part of writing Rust (and LLVM optimizations have finally been turned on: https://github.com/rust-lang/rust/issues/54878)

Also see https://github.com/rust-lang/rust/pull/103070 and https://reviews.llvm.org/D136659, which start introducing further Rust-specific optimizations.