Remove bad debt gas saving comment #584
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MerlinEgalite
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Nov 8, 2023
Rubilmax
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Nov 8, 2023
…-bad-debt-comment-1
Rubilmax
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Nov 11, 2023
MerlinEgalite
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Nov 11, 2023
The base branch was changed.
Jean-Grimal
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Nov 13, 2023
Rubilmax
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QGarchery
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I tested using forge, see the following POC
Gas test POC
// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity ^0.8.0;
import "../BaseTest.sol";
contract LiquidationGas is BaseTest {
uint256 constant ASSETS = 12 ether;
function setUp() public override {
super.setUp();
loanToken.setBalance(SUPPLIER, ASSETS);
collateralToken.setBalance(SUPPLIER, ASSETS);
vm.startPrank(SUPPLIER);
morpho.supply(marketParams, ASSETS, 0, SUPPLIER, "");
morpho.supplyCollateral(marketParams, ASSETS, SUPPLIER, "");
morpho.borrow(marketParams, ASSETS / 2, 0, SUPPLIER, SUPPLIER);
vm.stopPrank();
loanToken.setBalance(BORROWER, ASSETS);
collateralToken.setBalance(BORROWER, ASSETS);
vm.startPrank(BORROWER);
morpho.supply(marketParams, ASSETS, 0, BORROWER, "");
morpho.supplyCollateral(marketParams, ASSETS, BORROWER, "");
morpho.borrow(marketParams, ASSETS / 2, 0, BORROWER, BORROWER);
vm.stopPrank();
oracle.setPrice(ORACLE_PRICE_SCALE / 1000);
}
function testGasBadDebt() public {
vm.warp(block.timestamp + 30 days);
vm.startPrank(LIQUIDATOR);
morpho.liquidate(marketParams, BORROWER, ASSETS, 0, "");
vm.stopPrank();
}
}From this test, 2 factors stand out:
- it costs a lot in solidity to change slots, especially with packing because of the management of the slots. In assembly we could have written something that would be much more efficient, and it would make for more efficient bad debt realization. Note that I only tested without via-IR, so it may be more efficient in practice
- the blatant case where it does not save gas is if interest were already accrued (this is why there is the
vm.warpin the POC), because at this point the slottotalSupplyAssetsgets changed.
So in the end, I still think it saves gas (approximately 1.3k) in most cases. But I'm ok to remove that comment because it is more nuanced than what is currently written
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