Yep. A classic example is multiplication - which isn't constant-time on modern machines but was on many older ones. Currently, CMOV is looking like it could be

Yep. A classic example is multiplication - which isn't constant-time on modern machines but was on many older ones. Currently, CMOV is looking like it could become the same thing. It currently takes data-independent time. But is not guaranteed to do so, and very well may not in the future. The distinction is that hardware tends to change slower than software. You generally have multiple compiler versions per hardware version (possible exception of embedded processors, but even then...).