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GP seems to think it strange that "x86" would actually not have a performance difference here.

I think this might just be due to not realizing just how far back in CPU history this goes.

In a clockless cpu design you'd indeed expect xor to be faster. But in a regular CPU with a clock you either waste a bit of xor performance by making xor and sub both take the same number of ticks, or you speed up the clock enough that the speed difference between xor and sub justifies sub being at least a full tick slower

The former just seems way more practical

Even if they take the same number of ticks, shouldn't xor fundamentally needing less work also mean it can be performed while drawing less power/heating less, which is just as much an improvement in the long run?

That wasn’t much of a concern in the 70s and 80s.

Also, you probably spend much more energy moving the bits around the chip and out to RAM than you do on the actual calculation.

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