On 05/16/2017 08:41 PM, Jason Merrill wrote: > I agree that it makes sense to > check for a trivial assignment operator specifically. I guess we want > a slightly stronger "trivially copyable" that also requires a > non-deleted assignment operator. > > It seems to me that the relevant tests are: > > bcopy/memcpy/memmove want trivally copyable + non-deleted assignment. > bzero/memset want trivial + non-deleted assignment. > > I'm still not convinced we need to consider standard-layout at all.
What do you think of warning for memset of types with references? Since NULL references are undefined behavior (N4659, [dcl.ref]/5), IMHO such code is quite smelly and most likely a sign of incomplete refactoring, not design. (My original intention for poisoning memset of standard-layout type in gdb was mainly as proxy/approximation for "type with references". Other properties that make a type non-standard-layout are not as interesting to me.) While at it, maybe the same reasoning would justify warn of memcpy/memset of types with const data members? memcpy of such types kind of sounds like a recipe for subtle breakage that could only be salvaged with std::launder. And if you know about that, you'll probably be copying objects of type T to/from raw byte/char storage, not to/from another T. Actually, now that I look at Martin's new patch, I see he's already warning about const data members and references, both memcpy and memset. I'm not super convinced on warning about memcpy of references (unlike memset), but I don't feel strongly against it either. I'd be fine (FWIW) with giving it a try and see what breaks out there. > +Wnon-trivial-memaccess > +C++ ObjC++ Var(warn_nontrival_memaccess) Warning LangEnabledBy(C++ ObjC++, > Wall) > +Warn for raw memory writes to objects of non-trivial types. May I suggest renaming the warning (and the description above) from -Wnon-trivial-memaccess to something else that avoids "trivial" in its name? Because it's no longer strictly about "trivial" in the standard C++ sense. The documentation talks about "The safe way", and "does not warn on safe calls", so maybe call it -Wunsafe-memaccess? (I spotted a couple typos in the new patch: "otherwse", "becase", btw.) Thanks, Pedro Alves
