[Bug tree-optimization/122380] [15/16 regression] std::variant with std::vectors of differing types may lead to double frees since r15-5595

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122380

--- Comment #12 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
dse3 does:
```
  Deleted dead store: # .MEM_58 = VDEF <.MEM_57>
MEM[(struct _Vector_impl_data *)m_3(D) + 8B]._M_end_of_storage = 0B;

  Deleted dead store: # .MEM_57 = VDEF <.MEM_56>
MEM[(struct _Vector_impl_data *)m_3(D) + 8B]._M_finish = 0B;

  Deleted dead store: # .MEM_56 = VDEF <.MEM_52>
MEM[(struct _Vector_impl_data *)m_3(D) + 8B]._M_start = 0B;
```


`-O2 -fno-tree-pre ` works.