Definition size_compatible' (n: Z) (p: val) :=
match p with
| Vundef => True
| Vint _ => True
| Vlong _ => True
| Vfloat _ => True
| Vsingle _ => True
| Vptr _ i_ofs => Ptrofs.unsigned i_ofs + n < Ptrofs.modulus
end.

Lemma mapsto_force_ptr: forall sh t v v', mapsto sh t (force_ptr v) v' = mapsto sh t v v'.