https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671
--- Comment #27 from rguenther at suse dot de <rguenther at suse dot de> --- On Tue, 28 Feb 2017, jakub at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671 > > --- Comment #26 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > What about PODs or say int? Let's say I have a class with union in it and in > that union say float and char array, then use placement new an int with some > value into the char array in the union. What will then happen if I default > copy the class (default assignment operator or copy constructor)? The > following doesn't fail, but I think true_dependence still returns 0 for > (mem/c:SI (plus:DI (reg/f:DI 7 sp) > (const_int 4 [0x4])) [4 MEM[(int *)&b + 4B]+0 S4 A32]) > and > (mem:DI (reg/v/f:DI 0 ax [orig:87 p ] [87]) [1 MEM[(const struct B &)p_4]+0 S8 > A32]) > where the former is from the placement new store of int and the load is from > the structure assignment. > > inline void* operator new(__SIZE_TYPE__, void *p) { return p; } > struct B > { > float x; > union U > { > float a; > char b[sizeof (int)]; > } u; > float y; > }; > > __attribute__((noinline, noclone)) void > bar (B &x, B &y) > { > if (x.x != 0 || x.y != 3 || y.x != 0 || y.y != 3) > __builtin_abort (); > int f; > __builtin_memcpy (&f, x.u.b, sizeof (int)); > if (f != 81) > __builtin_abort (); > __builtin_memcpy (&f, y.u.b, sizeof (int)); > if (f != 81) > __builtin_abort (); > } > > __attribute__((noinline, noclone)) > B * > baz (B &x) > { > return &x; > } > > __attribute__((noinline, noclone)) void > foo (int x) > { > B b { 0.0f, {}, 3.0f }, c; > B *p = baz (b); > new (b.u.b) int (x); > c = *p; I don't think *p is of any type allowed to access the object of type int.
