https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671
--- Comment #52 from rguenther at suse dot de <rguenther at suse dot de> --- On Mon, 27 Mar 2017, bernd.edlinger at hotmail dot de wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671 > > --- Comment #51 from Bernd Edlinger <bernd.edlinger at hotmail dot de> --- > Doesn't 3.10/10 explicitly say that it is undefined to use a union to > to move an object representation that is not a member of the union? That was my reading... but 3.10/10 talks about "attempts to access the stored value of an object" and Jason says that this doesn't apply to d = *p but the result of the decomposition to memberwise copy plus union special handling (where it wouldn't apply at all) So the question (DR?) is whether 3.10/10 applies to the access as written in the source or to it after the decomposition happened. > "If a program attempts to access the stored value of an object through a > glvalue of other than one of the > following types the behavior is undefined:52 > — the dynamic type of the object, > — a cv-qualified version of the dynamic type of the object, > — a type similar (as defined in 4.4) to the dynamic type of the object, > — a type that is the signed or unsigned type corresponding to the dynamic type > of the object, > — a type that is the signed or unsigned type corresponding to a cv-qualified > version of the dynamic type > of the object, > — an aggregate or union type that includes one of the aforementioned types > among its elements or non- > static data members (including, recursively, an element or non-static data > member of a subaggregate > or contained union), > — a type that is a (possibly cv-qualified) base class type of the dynamic type > of the object, > — a char or unsigned char type."
