On Jun 19, 2011, at 4:24 PM, Eric Botcazou wrote: >> if T is a non-volatile composite type with volatile components, and O is an >> object of type T, are the optimizers allowed to remove the assignment "O := >> O"? > > Good question, that I'm not really qualified to answer. Any language lawyer?
I'd like to think that the optimizers are not allowed to remove the assignment (unless they synthesize of up the assignment of all volatile fields). For unions, head explodes. I think for unions, it can. I could check the standard to ensure I have it right, but, well, that's annoying. :-) This answer is for the answer for C and C++, but, the middle end, _could_ decide to differ, if it had a compelling reason to. I don't know of any reason. Now, before someone tries to optimize structures, please be very careful. Unions, transparent unions, frontend synthed structures with multiple offsets at the same location and the like come to mind.
