I'm not sure which comment you're responding to, because I'm not talking about shared_ptr, but about how atomic operations in general are implemented on x86.

I don't believe that shared_ptr uses seq-cst because I can just look at the source code, and I know that inc ref is relaxed and dec ref is acq-rel, as they should be.

However, none of this makes a difference on x86, where RMW atomic operations all lower to the same instructions (like LOCK ADD). Loads also do not care about memory order, and stores sometimes do, and that was what my comment was about.