"Compiler optimization" in this thread is referring to speeding up compilation time†, not runtime of generated code. Go produces fast code, but the go compiler does not generate that code particularly quickly.

† Which can be seen as a runtime cost for interpreter+JIT languages, but that's a different issue. We're talking time-to-steady-state when the interpreter is fed a file (which is something Javascript engine devs worry about a lot), not benchmark-speed-at-steady-state.