That's a different thing - the "sufficiently smart compiler" is postulating that it doesn't matter if a language is not very high performance because somehow magically there will one day be a compiler that can just figure out how to optimise the code in every case.

I'm just saying that in this particular case, sometimes the compiler will be able to optimise it but you can't rely on it.

https://godbolt.org/z/WshcfWPEh