Helge Bahmann wrote:
the standard says "should" not "must" -- the gcc guys have not made this decision without good reasons, and I agree with these reasons
It says "should" but only for the lock-free case: [ Note: Operations that are lock-free should also be address-free. That is, atomic operations on the same memory location via two different addresses will communicate atomically. The implementation should not depend on any per-process state. This restriction enables communication by memory that is mapped into a process more than once and by memory that is shared between two processes. —end note ] It also says: [ Note: the representation of an atomic specialization need not have the same size as its corresponding argument type. Specializations should have the same size whenever possible, as this reduces the effort required to port existing code. —end note ] The two recommendations are contradictory, so it's a quality of implementation issue.