Vulnerabilities of Ethereum smart contracts often cause serious financial damage. Whereas the Solidity compiler has been updated to prevent vulnerabilities, its effectiveness has not been revealed so far, to the best of our knowledge. In this paper, we shed light on the impact of compiler versions of vulnerabilities of Ethereum smart contracts. To this end, we collected 503,572 contracts with Solidity source codes in the Ethereum blockchain and then analyzed their vulnerabilities. For three vulnerabilities with high severity, i.e., Locked Money, Using tx.origin, and Unchecked Call, we show that their appearance rates are decreased by virtue of major updates of the Solidity compiler. We then found the following four key insights. First, after the release of version 0.6, the appearance rate for Locked Money has decreased. Second, regardless of compiler updates, the appearance rate for Using tx.origin is significantly low. Third, although the appearance rate for Unchecked Call has decreased in version 0.8, it still remains high due to various factors, including code clones. Fourth, through analysis of code clones, our promising results show that the appearance rate for Unchecked Call can be further decreased by removing the code clones.
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