> from the outside results are still guaranteed to be available in order - e.g. the instruction stream appears to be executed in order when observing the CPU from the outside.

> […]

> On some CPUs it does get tricky once memory is involved though (on ARM, but not on x86).

https://en.wikipedia.org/wiki/Memory_ordering:

“Among the commonly used architectures, x86-64 processors have the strongest memory order, but may still defer memory store instructions until after memory load instructions.”