I assume there is no extra cost to the extra subs/adds instructions, so there is no reason to perform this extra analysis when those are available. The author d

I assume there is no extra cost to the extra subs/adds instructions, so there is no reason to perform this extra analysis when those are available. The author does say: >In a VM, it isn’t able to configured the host CPU, so it can’t use this functionality. There are two other options. Either, you can skip computing the flags, because they’re mostly useless and most software won’t care. Or you can compute them the long way shown above. Rosetta 2 chooses the second option, and this mostly works out fine, because they have an “unused flags” optimisation that avoids the computation a lot of the time. So there's an optimization pass that does what you mentioned, it's just not needed when you have the right instruction available, and the thing is probably a wee bit faster if you don't do it.