[shakna]

> Furthermore, at every sequence point the value last stored in the object shall agree with that prescribed by the abstract machine, except as modified by the unknown factors mentioned previously.

I quoted the C standard, first. Not compiler behaviour.

I showed where it requires the compiler not to optimise this.

How about, instead of one-line throwaway disagreements, you point out where they are permitted to do this, instead?

[dwattttt]

The compiler is required to not optimise out reads/writes through volatile. That's unrelated to code also having UB: you can't sprinkle volatile through arbitrary UB and suddenly have it be defined.

> A compliant compiler is only free to optimise away, where it can determine there are no side-effects

A compliant compiler is also allowed to assume UB cannot occur.