https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117475
Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |UNCONFIRMED Resolution|INVALID |--- Ever confirmed|1 |0 --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Doing this: union U { S s{}; }; Works. So the problem is the testcase provided is invalid code but here is a testcase which works with clang but fails with GCC: ``` #include <atomic> typedef std::atomic_int Atomic_Int; struct S { Atomic_Int v; }; union U { int t = 0; S s; }; U obj; ```