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Clipper yank gas opt #175

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Jan 4, 2021
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Clipper yank gas opt #175

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9 changes: 4 additions & 5 deletions src/clip.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -356,12 +356,11 @@ contract Clipper {
emit SetBreaker(level);
}

// Cancel an auction during ES
// Cancel an auction during ES or via governance action.
function yank(uint id) external auth {
Sale memory sale = sales[id];
require(sale.usr != address(0), "Clipper/not-running-auction");
dog.digs(ilk, sale.tab);
vat.flux(ilk, address(this), msg.sender, sale.lot);
require(sales[id].usr != address(0), "Clipper/not-running-auction");
dog.digs(ilk, sales[id].tab);
vat.flux(ilk, address(this), msg.sender, sales[id].lot);
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curious if you tested the gas difference using the optimizer with a lot of runs?

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@kmbarry1 kmbarry1 Dec 17, 2020 •
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Well, I hadn't, but since you ask (using solc 0.6.7, with the note modifier bodies commented out since you can't compile with optimizations on if your code contains explicit mstore calls):

10^6 optimizer runs:
...whole struct read: 36,064
...per-field reads: 34,210

No optimization:
...whole struct read: 41,005
...per-fields reads: 38,296

So the optimizer does succeed in narrowing the gap, and (optimizations+whole struct read) is better than (no optimizations+per-field reads) but per-field reads is still better than a whole-struct read when optimizations are on. Btw bumping the runs up to 10^9 doesn't change them, so likely the numbers above are already the limit of the current optimizer's abilities.

_remove(id);
emit Yank();
}
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27 changes: 27 additions & 0 deletions src/test/clip.t.sol
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Expand Up @@ -876,4 +876,31 @@ contract ClipperTest is DSTest {
hevm.warp(startTime + 3601 seconds);
assertTrue( try_redo(1));
}

function test_Clipper_yank() public takeSetup {
uint256 preGemBalance = vat.gem(ilk, address(this));
(,, uint256 origLot,,,) = clip.sales(1);

uint startGas = gasleft();
clip.yank(1);
uint endGas = gasleft();
emit log_named_uint("yank gas", startGas - endGas);

// Assert that the auction was deleted.
(uint256 pos, uint256 tab, uint256 lot, address usr, uint256 tic, uint256 top) = clip.sales(1);
assertEq(pos, 0);
assertEq(tab, 0);
assertEq(lot, 0);
assertEq(usr, address(0));
assertEq(uint256(tic), 0);
assertEq(top, 0);

// Assert that callback to clear dirt was successful.
assertEq(dog.Dirt(), 0);
(,,, uint256 dirt,,) = dog.ilks(ilk);
assertEq(dirt, 0);

// Assert transfer of gem.
assertEq(vat.gem(ilk, address(this)), preGemBalance + origLot);
}
}