Proposed changes to PR #972:

- avoid calculating current LUP twice in lender kick
- change _kick function to accept proposed LUP (for regular kick proposed LUP is current LUP, for lender kick proposed LUP is calculated based on additional debt)
- in both kick cases return current LUP in kick result
- reduce gas costs by saving a Fenwick traversal
- reduce contract size by removing LUP calculation within Pool

src/base/Pool.sol

@@ -363,7 +363,7 @@ abstract contract Pool is Clone, ReentrancyGuard, Multicall, IPool {
         poolBalances.t0DebtInAuction = poolState.t0DebtInAuction;
 
         // update pool interest rate state
-        _updateInterestState(poolState, Deposits.getLup(deposits, poolState.debt));
+        _updateInterestState(poolState, result.lup);
 
         // transfer from kicker to pool the difference to cover bond
         if (result.amountToCoverBond != 0) _transferQuoteTokenFrom(msg.sender, result.amountToCoverBond);

src/libraries/external/KickerActions.sol

@@ -105,7 +105,7 @@ library KickerActions {
 
     /**
      *  @notice See `IPoolKickerActions` for descriptions.
-     *  @return The `KickResult` struct result of the kick action.
+     *  @return kickResult_ The `KickResult` struct result of the kick action.
      */
     function kick(
         AuctionsState storage auctions_,
@@ -115,17 +115,20 @@ library KickerActions {
         address borrowerAddress_,
         uint256 limitIndex_
     ) external returns (
-        KickResult memory
+        KickResult memory kickResult_
     ) {
-        return _kick(
+        uint256 curLup = Deposits.getLup(deposits_, poolState_.debt);
+
+        kickResult_ = _kick(
             auctions_,
-            deposits_,
             loans_,
             poolState_,
             borrowerAddress_,
             limitIndex_,
-            0
+            curLup // proposed LUP is the current pool LUP
         );
+        // return current LUP in pool
+        kickResult_.lup = curLup;
     }
 
     /**
@@ -151,7 +154,8 @@ library KickerActions {
         vars.bucketPrice = _priceAt(index_);
 
         // revert if the bucket price is below current LUP
-        if (vars.bucketPrice < Deposits.getLup(deposits_, poolState_.debt)) revert PriceBelowLUP();
+        uint256 curLup = Deposits.getLup(deposits_, poolState_.debt);
+        if (vars.bucketPrice < curLup) revert PriceBelowLUP();
 
         Bucket storage bucket = buckets_[index_];
         Lender storage lender = bucket.lenders[msg.sender];
@@ -175,16 +179,21 @@ library KickerActions {
         // revert if no entitled amount
         if (vars.entitledAmount == 0) revert InsufficientLiquidity();
 
+        // add amount to remove to pool debt in order to calculate proposed LUP
+        // this simulates LUP movement with additional debt
+        uint256 proposedLup =  Deposits.getLup(deposits_, poolState_.debt + vars.entitledAmount);
+
         // kick top borrower
         kickResult_ = _kick(
             auctions_,
-            deposits_,
             loans_,
             poolState_,
             Loans.getMax(loans_).borrower,
             limitIndex_,
-            vars.entitledAmount
+            proposedLup
         );
+        // return current LUP in pool
+        kickResult_.lup = curLup;
     }
 
     /*************************/
@@ -285,22 +294,20 @@ library KickerActions {
      *  @dev    === Emit events ===
      *  @dev    - `Kick`
      *  @param  auctions_        Struct for pool auctions state.
-     *  @param  deposits_        Struct for pool deposits state.
      *  @param  loans_           Struct for pool loans state.
      *  @param  poolState_       Current state of the pool.
      *  @param  borrowerAddress_ Address of the borrower to kick.
      *  @param  limitIndex_      Index of the lower bound of `NP` tolerated when kicking the auction.
-     *  @param  additionalDebt_  Additional debt to be used when calculating proposed `LUP`.
+     *  @param  proposedLup_     Proposed `LUP` in pool.
      *  @return kickResult_      The `KickResult` struct result of the kick action.
      */
     function _kick(
         AuctionsState storage auctions_,
-        DepositsState storage deposits_,
         LoansState    storage loans_,
         PoolState calldata poolState_,
         address borrowerAddress_,
         uint256 limitIndex_,
-        uint256 additionalDebt_
+        uint256 proposedLup_
     ) internal returns (
         KickResult memory kickResult_
     ) {
@@ -313,18 +320,13 @@ library KickerActions {
         kickResult_.t0KickedDebt        = borrower.t0Debt;
         kickResult_.collateralPreAction = borrower.collateral;
 
-        // add amount to remove to pool debt in order to calculate proposed LUP
-        // for regular kick this is the currrent LUP in pool
-        // for provisional kick this simulates LUP movement with additional debt
-        kickResult_.lup = Deposits.getLup(deposits_, poolState_.debt + additionalDebt_);
-
         KickLocalVars memory vars;
         vars.borrowerDebt       = Maths.wmul(kickResult_.t0KickedDebt, poolState_.inflator);
         vars.borrowerCollateral = kickResult_.collateralPreAction;
         vars.borrowerNpTpRatio  = borrower.npTpRatio;
 
         // revert if kick on a collateralized borrower
-        if (_isCollateralized(vars.borrowerDebt, vars.borrowerCollateral, kickResult_.lup, poolState_.poolType)) {
+        if (_isCollateralized(vars.borrowerDebt, vars.borrowerCollateral, proposedLup_, poolState_.poolType)) {
             revert BorrowerOk();
         }