Using extcodehash instead of extcodesize for less gas

[PhABC]

extcodehash uses less gas then extcodesize. You can tell which address is a contract by the hash (see EIP-1052).

Fixes #

[nventuro]

Thank you @PhABC! extcodehash uses 400 gas, while extcodesize uses 700. I did a quick test in Remix and this version does indeed seem to be cheaper, while preserving semantics.

We should add a comment explaining what 0x0 and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 mean: they are the codehashes for a new account, and an account with no code respectively. I assume 'new account' means an account that has not been targeted by any transaction, but I'm not entirely sure of this.

Also, could you add a changelog entry for this improvement? Thanks!

[PhABC]

@nventuro Added comments! Not sure where to add a changelog entry however.

[frangio]

Oh wow, it's super interesting that it returns two different values depending if the account has been used or not! I wonder if this distinction can be used for something?

@PhABC The changelog entry should go in CHANGELOG.md, under a subsection "Improvements" for the last version.

[stale]

Hi all!
This Pull Request has not had any recent activity, is it still relevant? If so, what is blocking it? Is there anything we can do to help move it forward?
Thanks!

[frangio]

Added the changelog entry. Thank you @PhABC!

[juli]

This isContract code using EXTCODEHASH is not cheaper, consider changing it back to EXTCODESIZE if there isn't any other known benefit.
The gas cost savings (if any, not counting keccak256 constant deployment cost) were short-lived, EXTCODEHASH gas cost was changed to 700 by EIP-1884.

References:
EIP-1884
go-ethereum commit
Solidity compiler issue
Solidity CALL compiler code

[Amxx]

Note: EIP-2929 affect pricing of these opcodes.

Gas cost for both operations is the same:

• 100 if the queried entry is in touched_storage_slots (warm access)
• 2100 if the queried entry is in not touched_storage_slots (cold access)