BALANCE opcode must return a different value for the origin account

[Lohann]

Crate version: v0.41.0

Related: #222
While using this EVM to sync with ethereum mainnet, I've a found a sync mismatch when processing the transaction at block 165514:
https://etherscan.io/tx/0xe01fcce5f0fb0d04d253908ebadbada9308731a8bd0d1f1b37ad3af111e6a055

Issue

The BALANCE Opcode must return a different balance for the origin account (a.k.a. tx signer), instead of returning the actual balance, it must return the worst case balance for this account, which is balance - (tx.gasPrice * tx.gasLimit), because the transaction is being processed, and we don't know the final the balance.

Example contract:

ORIGIN # or CALLER, once they are the same here
BALANCE
PUSH1 0x00
SSTORE
STOP

Expected Behavior:

before execute transaction: 0x47e512b02979c8b8
returned by BALANCE opcode: 0x47336ff3fab4c8b8 == balance - (gas_price * gas_limit)
after apply state changes: 0x47c014fbdbd794b8 == balance - (gas_price * gas_used)

Actual behavior:

before execute transaction: 0x47e512b02979c8b8
returned by BALANCE opcode: 0x47e512b02979c8b8
after apply state changes: 0x47c014fbdbd794b8

Workaround

Decrement the tx sender balance before execute the tx,and increment again after apply the state changes.

[sorpaas]

I think this is fixed in the next branch, but I'll keep this in note and make sure it's actually the case!