[talaketu]

> more efficient code that does the same thing

In this case, it produces a different result.

[masklinn]

It produces a different ub, which is ub.

Furthermore observability would be defined in terms of the C abstract machine, “observing” by decompiling the program is out of scope.

[talaketu]

oh right

> But what if you're not using C99 or newer?

UB - that takes all the fun out of it.