Definition compat_pointer_chunks (chunk1 chunk2: memory_chunk) : Prop :=
  match chunk1, chunk2 with
  | (Mint32 | Many32), (Mint32 | Many32) => True
  | (Mint64 | Many64), (Mint64 | Many64) => True
  | _, _ => False
  end.

Theorem store_int8_sign_ext: forall m b ofs n, store Mint8signed m b ofs (Vint (Int.sign_ext 8 n)) = store Mint8signed m b ofs (Vint n).