I see the msvc arm compiler has not improved much in 20 years. The msvc arm was pretty odd when we used it in ~2003. We did not trust it at all. Think we had to get 4 or so compiler fixes out of MS for that project plus 3 or 4 library fixes. The x86 one was pretty solid. We were targeting 4 different CPU platforms at the same time so we could find things like that decently quickly. Most of the the time it was something we did that was weird. But even then we would find them. That one looks like maybe the optimizer back filled a nop slot?