You get it. That's exactly what I'm referring to. But - moving values between registers (or between a register and the stack) is crazy fast anyway. I'd love to

You get it. That's exactly what I'm referring to. But - moving values between registers (or between a register and the stack) is crazy fast anyway. I'd love to see some benchmarks showing how much of a difference this optimisation would make in practice. It's fast, but the instructions still occupy space in caches, memory, and decoders; space that could've been used for other more valuable instructions. The problem is that the typical microbenchmarks don't show this sort of inefficiency (and on the other hand makes questionable-at-large options like loop unrolling seem great), because they're too small to see the effects of the waste.