Cache storage variables in the stack can save gas

[code423n4]

Handle

WatchPug

Vulnerability details

For the storage variables that will be accessed multiple times, cache them in the stack can save ~100 gas from each extra read (SLOAD after Berlin).

For example:

• scheduled[hashTx] in QuickAccManager.sol#cancel() https://github.com/code-423n4/2021-10-ambire/blob/bc01af4df3f70d1629c4e22a72c19e6a814db70d/contracts/wallet/QuickAccManager.sol#L92-L92

• scheduled[hash] in QuickAccManager.sol#execScheduled() https://github.com/code-423n4/2021-10-ambire/blob/bc01af4df3f70d1629c4e22a72c19e6a814db70d/contracts/wallet/QuickAccManager.sol#L102-L102

[Ivshti]

resolved in https://github.com/AmbireTech/adex-protocol-eth/commit/b2a799ea7b43039b3ac47fb27b395b8f8da378ee

[GalloDaSballo]

As per eip-2929 the cost of reading a cold storage slot is 2100, the cost of reading from a hot storage slot (already read once) is 100

While apparently minor, storing the result of the read in memory will end up saving 94 gas (3 gas to MSTORE, 3 gas to MLOAD) when compared to re-reading from Storage

[GalloDaSballo]

The sponsor has applied the improvement