Slightly reduce ERC721 deployment gas cost

🧐 Motivation

ERC721.sol

Changing the order of arguments of first require in approve function can slightly reduce fuel costs for contract deploy.

📝 Details

In function

/**
 * @dev See {IERC721-approve}.
 */
function approve(address to, uint256 tokenId) public virtual override {
    address owner = ERC721.ownerOf(tokenId);
    require(to != owner, "ERC721: approval to current owner");


    require(_msgSender() == owner || isApprovedForAll(owner, _msgSender()),
        "ERC721: approve caller is not owner nor approved for all"
    );


    _approve(to, tokenId);
}

Changing the line

    require(to != owner, "ERC721: approval to current owner");

to

    require(owner != to, "ERC721: approval to current owner");

may lead to a minor decrease in gas cost at deployment. I think the reason is more efficient work with stack. This does not affect the gas consumption at function call.

[frangio]

@vladyan18 Can you report these over in the Solidity repository? It seems it should be the responsibility of the optimizer to do this.

[Amxx]

Adding unchecked blocks was considered during the 4.0 dev phase. It was put on hold, but we should probably reconsider it.