[jbert]

Can you play the game the other way and "fail safe"?

i.e. declare the storage volatile but running your crypto code on a non-volatile ptr to it (obtained via cast) to get your performance back?

If the compiler then generates enough smarts to work out that the non-volatile ptr you've passed into your crypto code is referring to volatile storage, then you keep security but get a (noticeable in testing?) performance hit.

I guess that's not as good as your solution though.