Out-of-order instruction execution: is commit order preserved?
TL:DR: memory ordering is not the same thing as out of order execution. It happens even on in-order pipelined CPUs. In-order commit is necessary1 for precise exceptions that can roll-back to exactly the instruction that faulted, without any instructions after that having already retired. The cardinal rule of out-of-order execution is don’t break single-threaded code. … Read more