small lending pool gas optimization

contracts/lendingpool/LendingPool.sol

@@ -92,22 +92,21 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
 
     ValidationLogic.validateDeposit(reserve, amount);
 
-    IAToken aToken = IAToken(reserve.aTokenAddress);
+    address aToken = reserve.aTokenAddress;
-
-    bool isFirstDeposit = aToken.balanceOf(msg.sender) == 0;
 
     reserve.updateCumulativeIndexesAndTimestamp();
-    reserve.updateInterestRates(asset, amount, 0);
+    reserve.updateInterestRates(asset, aToken, amount, 0);
 
+    bool isFirstDeposit = IAToken(aToken).balanceOf(msg.sender) == 0;
     if (isFirstDeposit) {
       _usersConfig[msg.sender].setUsingAsCollateral(reserve.index, true);
     }
 
     //minting AToken to user 1:1 with the specific exchange rate
-    aToken.mint(msg.sender, amount);
+    IAToken(aToken).mint(msg.sender, amount);
 
     //transfer to the aToken contract
-    IERC20(asset).safeTransferFrom(msg.sender, address(aToken), amount);
+    IERC20(asset).safeTransferFrom(msg.sender, aToken, amount);
 
     //solium-disable-next-line
     emit Deposit(asset, msg.sender, amount, referralCode);
@@ -121,9 +120,9 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
   function withdraw(address asset, uint256 amount) external override nonReentrant {
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
-    IAToken aToken = IAToken(reserve.aTokenAddress);
+    address aToken = reserve.aTokenAddress;
 
-    uint256 userBalance = aToken.balanceOf(msg.sender);
+    uint256 userBalance = IAToken(aToken).balanceOf(msg.sender);
 
     uint256 amountToWithdraw = amount;
 
@@ -134,7 +133,7 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
 
     ValidationLogic.validateWithdraw(
       asset,
-      address(aToken),
+      aToken,
       amountToWithdraw,
       userBalance,
       _reserves,
@@ -145,13 +144,13 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
 
     reserve.updateCumulativeIndexesAndTimestamp();
 
-    reserve.updateInterestRates(asset, 0, amountToWithdraw);
+    reserve.updateInterestRates(asset, aToken, 0, amountToWithdraw);
 
     if (amountToWithdraw == userBalance) {
       _usersConfig[msg.sender].setUsingAsCollateral(reserve.index, false);
     }
 
-    aToken.burn(msg.sender, msg.sender, amountToWithdraw);
+    IAToken(aToken).burn(msg.sender, msg.sender, amountToWithdraw);
 
     //solium-disable-next-line
     emit Withdraw(asset, msg.sender, amount);
@@ -202,14 +201,16 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
       IVariableDebtToken(reserve.variableDebtTokenAddress).mint(msg.sender, amount);
     }
 
-    reserve.updateInterestRates(asset, 0, amount);
+    address aToken = reserve.aTokenAddress;
+    reserve.updateInterestRates(asset, aToken, 0, amount);
 
-    if (!userConfig.isBorrowing(reserve.index)) {
+    uint256 reserveIndex = reserve.index;
-      userConfig.setBorrowing(reserve.index, true);
+    if (!userConfig.isBorrowing(reserveIndex)) {
+      userConfig.setBorrowing(reserveIndex, true);
     }
 
     //if we reached this point, we can transfer
-    IAToken(reserve.aTokenAddress).transferUnderlyingTo(msg.sender, amount);
+    IAToken(aToken).transferUnderlyingTo(msg.sender, amount);
 
     emit Borrow(
       asset,
@@ -270,13 +271,14 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
       IVariableDebtToken(reserve.variableDebtTokenAddress).burn(onBehalfOf, paybackAmount);
     }
 
-    reserve.updateInterestRates(asset, paybackAmount, 0);
+    address aToken = reserve.aTokenAddress;
+    reserve.updateInterestRates(asset, aToken, paybackAmount, 0);
 
     if (stableDebt.add(variableDebt).sub(paybackAmount) == 0) {
       _usersConfig[onBehalfOf].setBorrowing(reserve.index, false);
     }
 
-    IERC20(asset).safeTransferFrom(msg.sender, reserve.aTokenAddress, paybackAmount);
+    IERC20(asset).safeTransferFrom(msg.sender, aToken, paybackAmount);
 
     emit Repay(asset, onBehalfOf, msg.sender, paybackAmount);
   }
@@ -317,7 +319,7 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
       );
     }
 
-    reserve.updateInterestRates(asset, 0, 0);
+    reserve.updateInterestRates(asset, reserve.aTokenAddress, 0, 0);
 
     emit Swap(
       asset,
@@ -367,7 +369,7 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
     stableDebtToken.burn(user, stableBorrowBalance);
     stableDebtToken.mint(user, stableBorrowBalance, reserve.currentStableBorrowRate);
 
-    reserve.updateInterestRates(asset, 0, 0);
+    reserve.updateInterestRates(asset, reserve.aTokenAddress, 0, 0);
 
     emit RebalanceStableBorrowRate(asset, user);
 
@@ -501,7 +503,7 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable, ILendingPool {
     reserve.cumulateToLiquidityIndex(totalLiquidityBefore, amountFee);
 
     //refresh interest rates
-    reserve.updateInterestRates(asset, amountFee, 0);
+    reserve.updateInterestRates(asset, aTokenAddress, amountFee, 0);
 
     //solium-disable-next-line
     emit FlashLoan(receiverAddress, asset, amount, amountFee);

contracts/lendingpool/LendingPoolLiquidationManager.sol

@@ -136,7 +136,9 @@ contract LendingPoolLiquidationManager is ReentrancyGuard, VersionedInitializabl
       );
     }
 
-    vars.userCollateralBalance = IERC20(collateralReserve.aTokenAddress).balanceOf(user);
+    vars.collateralAtoken = IAToken(collateralReserve.aTokenAddress);
+
+    vars.userCollateralBalance = vars.collateralAtoken.balanceOf(user);
 
     vars.isCollateralEnabled =
       collateralReserve.configuration.getLiquidationThreshold() > 0 &&
@@ -192,8 +194,6 @@ contract LendingPoolLiquidationManager is ReentrancyGuard, VersionedInitializabl
       vars.actualAmountToLiquidate = vars.principalAmountNeeded;
     }
 
-    vars.collateralAtoken = IAToken(collateralReserve.aTokenAddress);
-
     //if liquidator reclaims the underlying asset, we make sure there is enough available collateral in the reserve
     if (!receiveAToken) {
       uint256 currentAvailableCollateral = IERC20(collateral).balanceOf(
@@ -209,7 +209,12 @@ contract LendingPoolLiquidationManager is ReentrancyGuard, VersionedInitializabl
 
     //update the principal reserve
     principalReserve.updateCumulativeIndexesAndTimestamp();
-    principalReserve.updateInterestRates(principal, vars.actualAmountToLiquidate, 0);
+    principalReserve.updateInterestRates(
+      principal,
+      principalReserve.aTokenAddress,
+      vars.actualAmountToLiquidate,
+      0
+    );
 
     if (vars.userVariableDebt >= vars.actualAmountToLiquidate) {
       IVariableDebtToken(principalReserve.variableDebtTokenAddress).burn(
@@ -235,7 +240,12 @@ contract LendingPoolLiquidationManager is ReentrancyGuard, VersionedInitializabl
 
       //updating collateral reserve
       collateralReserve.updateCumulativeIndexesAndTimestamp();
-      collateralReserve.updateInterestRates(collateral, 0, vars.maxCollateralToLiquidate);
+      collateralReserve.updateInterestRates(
+        collateral,
+        address(vars.collateralAtoken),
+        0,
+        vars.maxCollateralToLiquidate
+      );
 
       //burn the equivalent amount of atoken
       vars.collateralAtoken.burn(user, msg.sender, vars.maxCollateralToLiquidate);

contracts/libraries/logic/ReserveLogic.sol

@@ -126,18 +126,18 @@ library ReserveLogic {
       IERC20(reserve.variableDebtTokenAddress).totalSupply() > 0 ||
       IERC20(reserve.stableDebtTokenAddress).totalSupply() > 0
     ) {
+      uint40 lastUpdateTimestamp = reserve.lastUpdateTimestamp;
+
       uint256 cumulatedLiquidityInterest = MathUtils.calculateLinearInterest(
         reserve.currentLiquidityRate,
-        reserve.lastUpdateTimestamp
+        lastUpdateTimestamp
       );
 
-      reserve.lastLiquidityIndex = cumulatedLiquidityInterest.rayMul(
+      reserve.lastLiquidityIndex = cumulatedLiquidityInterest.rayMul(reserve.lastLiquidityIndex);
-        reserve.lastLiquidityIndex
-      );
 
       uint256 cumulatedVariableBorrowInterest = MathUtils.calculateCompoundedInterest(
         reserve.currentVariableBorrowRate,
-        reserve.lastUpdateTimestamp
+        lastUpdateTimestamp
       );
       reserve.lastVariableBorrowIndex = cumulatedVariableBorrowInterest.rayMul(
         reserve.lastVariableBorrowIndex
@@ -164,9 +164,7 @@ library ReserveLogic {
 
     uint256 cumulatedLiquidity = amountToLiquidityRatio.add(WadRayMath.ray());
 
-    reserve.lastLiquidityIndex = cumulatedLiquidity.rayMul(
+    reserve.lastLiquidityIndex = cumulatedLiquidity.rayMul(reserve.lastLiquidityIndex);
-      reserve.lastLiquidityIndex
-    );
   }
 
   /**
@@ -208,21 +206,20 @@ library ReserveLogic {
   function updateInterestRates(
     ReserveData storage reserve,
     address reserveAddress,
+    address aTokenAddress,
     uint256 liquidityAdded,
     uint256 liquidityTaken
   ) internal {
     uint256 currentAvgStableRate = IStableDebtToken(reserve.stableDebtTokenAddress)
       .getAverageStableRate();
 
-    uint256 balance = IERC20(reserveAddress).balanceOf(reserve.aTokenAddress);
-
     (
       uint256 newLiquidityRate,
       uint256 newStableRate,
       uint256 newVariableRate
     ) = IReserveInterestRateStrategy(reserve.interestRateStrategyAddress).calculateInterestRates(
       reserveAddress,
-      balance.add(liquidityAdded).sub(liquidityTaken),
+      IERC20(reserveAddress).balanceOf(aTokenAddress).add(liquidityAdded).sub(liquidityTaken),
       IERC20(reserve.stableDebtTokenAddress).totalSupply(),
       IERC20(reserve.variableDebtTokenAddress).totalSupply(),
       currentAvgStableRate