Array length cache PoC

Audit.t.sol

pragma solidity ^0.8.17;

import "forge-std/Test.sol";
import "forge-std/console2.sol";

contract AuditTest is Test {

    address[] array;

    function setUp() external {
        array.push(address(1)); 
        array.push(address(2)); 
        array.push(address(3)); 
        array.push(address(4)); 
        array.push(address(5)); 
        array.push(address(6)); 
        array.push(address(7)); 
        array.push(address(8)); 
        array.push(address(9)); 
        array.push(address(10));
    }

    function test_AccessArrayLengthFromStorage() external {

        // No cache

        uint256 gasB4 = gasleft();
        for(uint i; i < array.length; i++) {
            // Do smth
        }
        uint256 gasConsumed = gasB4 - gasleft();

        // Cache

        uint256 length = array.length;
        uint256 _gasB4 = gasleft();
        for(uint i; i < length; i++) {
            // Do smth
        }
        uint256 _gasConsumed = _gasB4 - gasleft();

        console2.log("No cache gas consumed: ", gasConsumed);                                   // 4252
        console2.log("Cache gas consumed: ", _gasConsumed);                                     // 1152
        console2.log("Absolute diff: %d ", gasConsumed - _gasConsumed);                         // 3100
        console2.log("Relative diff: %d% ", (gasConsumed - _gasConsumed) * 100 / gasConsumed);  // 72%
    }

}

instructions.txt

1. Add the above file to /test
2. Execute it with `forge t --mc AuditTest -vv`