Every time there's an indirect branch (including a return) there's a chance that they will be inspected. The "unused flags" optimisation does remove most of the

Every time there's an indirect branch (including a return) there's a chance that they will be inspected. The "unused flags" optimisation does remove most of them, in a way that gets it right 100% of the time (excluding signals/interrupts inspecting state at random points, and possible bugs), but the pattern "an add or subtract or compare followed by an indirect branch or return" is still very common. (I haven't looked at Linux Rosetta 2, other than to note the parity-flag computation coincidentally showing up in a screenshot posted to Twitter, so I'm not sure exactly how often they do the manual computation, but I'm guessing it's anywhere flags are used, in which case the unused-flags optimisation could be extended further by tracking AF and PF separately to the usual flags, which is roughly your suggestion.) You could still remove the vast majority of the remaining computations with some heuristics that work well, but then you've gone from 100% correct to 99.9% correct, which is nice to avoid when you have the option.