perf: assembly optimisations (Finding 8) (#43)

* perf: write `Create2` revert data to the beginning of memory * perf: assembly for all of `ERC721TransferLib._transfer()` with reusable data
ARR4N · Aug 4, 2024 · 8f51558 · 8f51558
1 parent fb56fb7
commit 8f51558
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Showing 2 changed files with 15 additions and 20 deletions.
diff --git a/src/Create2.sol b/src/Create2.sol
@@ -23,15 +23,15 @@ library Create2 {
         }
 
         assembly ("memory-safe") {
-            let free := mload(0x40)
-
             if iszero(returndatasize()) {
-                mstore(free, 0x33d2bae4) // Create2EmptyRevert()
-                revert(add(free, 28), 4)
+                mstore(0, 0x33d2bae4) // Create2EmptyRevert()
+                revert(28, 4)
             }
 
-            returndatacopy(free, 0, returndatasize())
-            revert(free, returndatasize())
+            // Even though this may extend beyond scratch space, we revert the current context immediately so it's still
+            // memory-safe.
+            returndatacopy(0, 0, returndatasize())
+            revert(0, returndatasize())
         }
     }
 }
diff --git a/src/ERC721TransferLib.sol b/src/ERC721TransferLib.sol
@@ -71,24 +71,19 @@ library ERC721TransferLib {
         }
         uint256[] memory ids = token.ids;
 
-        uint256 idSrc;
-        uint256 idDst;
         assembly ("memory-safe") {
-            idSrc := add(ids, 0x20)
-            idDst := add(reusableCallData, 0x64)
-        }
+            let idSrc := add(ids, 0x20)
+            let idDst := add(reusableCallData, 0x64)
+            let dataPtr := add(reusableCallData, 0x20)
 
-        for (uint256 end = idSrc + ids.length * 0x20; idSrc < end; idSrc += 0x20) {
-            assembly ("memory-safe") {
+            for { let end := add(idSrc, mul(mload(ids), 0x20)) } lt(idSrc, end) { idSrc := add(idSrc, 0x20) } {
                 mcopy(idDst, idSrc, 0x20)
-            }
-            (bool success,) = addr.call(reusableCallData);
 
-            if (!success) {
-                assembly ("memory-safe") {
-                    let free := mload(0x40)
-                    returndatacopy(free, 0, returndatasize())
-                    revert(free, returndatasize())
+                if iszero(call(gas(), addr, 0, dataPtr, reusableCallData, 0, 0)) {
+                    // Even though this may extend beyond scratch space, we revert the current context immediately so
+                    // it's still memory-safe.
+                    returndatacopy(0, 0, returndatasize())
+                    revert(0, returndatasize())
                 }
             }
         }