Reuse existing storage variables' cache can save gas

[code423n4]

Handle

WatchPug

Vulnerability details

https://github.com/code-423n4/2022-01-trader-joe/blob/a1579f6453bc4bf9fb0db9c627beaa41135438ed/contracts/LaunchEvent.sol#L377-L435

function createPair() external isStopped(false) atPhase(Phase.PhaseThree) {
    (address wavaxAddress, address tokenAddress) = (
        address(WAVAX),
        address(token)
    );
    // ...
    if (
        floorPrice > (wavaxReserve * 10**token.decimals()) / tokenAllocated
    ) {
        tokenAllocated = (wavaxReserve * 10**token.decimals()) / floorPrice;
        // ...
    }

    WAVAX.approve(address(router), wavaxReserve);
    token.approve(address(router), tokenAllocated);
    // ...
}

• WAVAX at L407 is already cached in the local variable wavaxAddress at L378 ~ L379.
• token at L396, L398, L408 is already cached in the local variable tokenAddress at L378 ~ L380.

Reusing the cached local variable instead of reading from storage again can save gas.

Read from the stack can save ~100 gas from each extra read (SLOAD after Berlin).

[cryptofish7]

Duplicate of #236