[GeertB]

Having been there, and having bitten often enough, I can confirm that most compilers just try to generate the most conservative code possible for volatile accesses. Their semantics are crazy/inconsistent, so you can't reason about them, and high performance code won't use them. Nobody will ever be interested in making them work/perform well.

C++ atomics in their various memory models are different in that they have well-defined semantics, used in high performance code and people do care. You're right that there have been bugs (and probably still are), but at least you can _argue_ that something is a bug if there is a coherent definition. Optimization of atomics, such as merging barriers, is still in its infancy.