https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112480
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Andrew Pinski from comment #3) > I think that is because that transformation would violate the memory model > of C++. Ah yes. It would be safe for another thread to read the same memory location, as long as they all read false so that no store to that location happens. If we introduce a store, reads in other threads would conflict and we would have a data race, i.e. undefined behaviour. What the compiler doesn't know is that the standard already forbids any potentially concurrent access, because _M_reset() is a non-const member function. So we can force the store to happen, as we know it's ok where the compiler doesn't.
