Unless you are building your own custom kernel (ie gentoo) CPU specific optimizations are not worth it as they are worse for any other CPU even if the code is still run. Most software never had those micro optimizations applied, because most software wants to have one build that runs any many different CPUs, but if you want to make an exception it is still possible with compiled code.

While you can write those micro optimizations for each CPU by hand, they not worth the human cost except in very rare situations. In most cases of course you can't measure the difference, as only a couple CPU cycles are saved.