I'm very sorry, yes, you are right of course the load is still there. I was so fixated in producing a minimal test case that I failed to interpret the result.

I'm very sorry, yes, you are right of course the load is still there. I was so fixated in producing a minimal test case that I failed to interpret the result. Now I'm not able to reproduce the issue with a guaranteed UB. I still think the loop variant shows the same problem though. In any case, yes, according to the C standard a volatile read counts as an observable side effect.