https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69148
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- And union U { int r; float f; }; struct A { int a; union U b[64]; }; double foo (double); void bar (struct A *z, int x) { union U y; y.f = foo (z->b[x].f); z->a = y.r ? 4 : y.r; } too (to make it C rather than C++).