Saving deployment costs of smart contracts by eliminating gas-wasteful patterns

Smart contracts are blockchain-based programs that have developed with the emergence of Ethereum, one of the most well-known blockchains. Gas, paid in Ethers (i.e., the cryptocurrency in Ethereum), is required for the costs to upload and run smart contracts on Ethereum. As cost-inefficiently designed smart contracts result in unnecessary costs, it is vital to eliminate any gas-wasteful code fragments to optimize the deployment costs. In this study, we define five gas-wasteful patterns: ‘Over-public variables’, ‘Redundant initial values’, ‘Loose packing’, ‘Non-base unit types’, and ‘Non-constant variables’, based on the state variables in Solidity, the most commonly used implementation language for smart contracts in Ethereum. We also propose improvement methods related to these patterns and a solution to identify and eliminate the patterns. Furthermore, we analyze 143 real-world contracts deployed on Ethereum and find that 56% of them include the above-mentioned patterns. We also upgrade 43 of the pattern-matched contracts and demonstrate that their deployment costs are decreased on an average by 13.47%, and the most-reduced rate is 64%.