Rust using the LLVM toolchain is a real plus, which Clang also uses in the C++ world. The Clang and Rust compilers are basically frontends to LLVM, and any language that compiles using LLVM is translated to IR (intermediate representation). All code optimization is done on the IR code itself in LLVM, which both Rust and C++ compile down to before being compiled further into assembly. That means that the same effort that goes into optimization in the C++ world for Clang is shared by the Rust community too, and any other compiler that uses LLVM.