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:

• troveManager in TroveManagerRedemptions#_updateBaseRateFromRedemption()

  https://github.com/code-423n4/2021-12-yetifinance/blob/5f5bf61209b722ba568623d8446111b1ea5cb61c/packages/contracts/contracts/TroveManagerRedemptions.sol#L432-L447

  function _updateBaseRateFromRedemption(uint256 _YUSDDrawn, uint256 _totalYUSDSupply)
  internal
  returns (uint256)
  {
      uint256 decayedBaseRate = troveManager.calcDecayedBaseRate();
  
      /* Convert the drawn Collateral back to YUSD at face value rate (1 YUSD:1 USD), in order to get
       * the fraction of total supply that was redeemed at face value. */
      uint256 redeemedYUSDFraction = _YUSDDrawn.mul(10**18).div(_totalYUSDSupply);
  
      uint256 newBaseRate = decayedBaseRate.add(redeemedYUSDFraction.div(BETA));
      newBaseRate = LiquityMath._min(newBaseRate, DECIMAL_PRECISION); // cap baseRate at a maximum of 100%
  
      troveManager.updateBaseRate(newBaseRate);
      return newBaseRate;
  }