Does the C++ volatile keyword introduce a memory fence?

Question

I understand that volatile informs the compiler that the value may be changed, but in order to accomplish this functionality, does the compiler need to introduc

Answer 1

The compiler needs to introduce a memory fence around volatile accesses if, and only if, that is necessary to make the uses for volatile specified in the standard work (setjmp, signal handlers, and so on) on that particular platform.

Note that some compilers do go way beyond what's required by the C++ standard in order to make volatile more powerful or useful on those platforms. Portable code shouldn't rely on volatile to do anything beyond what's specified in the C++ standard.