Account Existence check

[wolflo]

Summary of the problem

Account existence is inconsistent with EIP-161. Accounts can remain existent-but-empty, which should not be the case.

Manticore version

0.3.4

Python version

3.8.5

Step to reproduce the behavior

The following test shows the issue as it relates to calculation of the gas cost for a self-destruct instruction. Account 0xffffffffffffffffffffffffffffffffffffffff is touched in the first transaction, but should remain non-existent because it has no code, zero balance, and zero nonce. The self-destruct in the second transaction should charge 21000 + 3 + 5000 + 25000 - 24000, but instead charges 21000 + 3 + 5000 - min(gas_used / 2, 24000) = 13002 because the recipient account is considered as already existing.

def test_acct_existence(self):
    with disposable_mevm() as m:
        asm_acc = """   PUSH20 0xffffffffffffffffffffffffffffffffffffffff
                        SELFDESTRUCT
                  """

        # 21000 base tx + 3 push op + 5000 base selfdestruct + 25000 new acct cost - 24000 refund
        expected_gas = 27003

        m.create_account(
            address=0x111111111111111111111111111111111111111,
            code=EVMAsm.assemble(asm_acc),
            balance=1
        )
        m.create_account(
            address=0x222222222222222222222222222222222222222,
            balance=1000000000000000000
        )

        # this should not result in creation of the acct, but does
        m.transaction(
            caller=0x222222222222222222222222222222222222222,
            address=0xffffffffffffffffffffffffffffffffffffffff,
            data=b'',
            value=0
        )
        # this should result in creation of the acct, but it's already created
        m.transaction(
            caller=0x222222222222222222222222222222222222222,
            address=0x111111111111111111111111111111111111111,
            data=b'',
            value=0
        )
        self.assertEqual(m.count_ready_states(), 1)
        state = next(m.ready_states)
        txs = state.platform.transactions

        # AssertionError: 13002 != 27003
        self.assertEqual(txs[-1].used_gas, expected_gas)

Expected behavior

An account that is touched but remains empty should be considered non-existent.

Actual behavior

Touched accounts are considered existing regardless of code, nonce, and balance.