Adjust data section size during creation.

test/libsolidity/semanticTests/salted_create/prediction_example.sol

@@ -5,14 +5,31 @@ contract D {
     }
 }
 
+// TODO: this is horrible and hopefully avoided at the spec level
+function adjustContractCodeForArgSize(bytes memory x, uint16 argSize)
+{
+  assembly {
+	let memPos := add(x, 32)
+	let numCodeSections := shr(240, mload(add(memPos, 7)))
+	let dataSectionSizeOffset := add(memPos, add(10, mul(numCodeSections, 2)))
+	let tmp := mload(dataSectionSizeOffset)
+	let dataSectionSize := shr(240, tmp)
+	dataSectionSize := add(dataSectionSize, argSize)
+	if gt(dataSectionSize, 0xFFFF) { revert(0,0) }
+	mstore(dataSectionSizeOffset, or(shr(16, shl(16, tmp)), shl(240, dataSectionSize)))
+  }
+}
+
 contract C {
     function createDSalted(bytes32 salt, uint arg) public {
+        bytes memory creationCode = type(D).creationCode;
+	adjustContractCodeForArgSize(creationCode, 32);
         address predictedAddress = address(uint160(uint(keccak256(abi.encodePacked(
             bytes1(0xff),
             address(this),
             salt,
             keccak256(abi.encodePacked(
-                type(D).creationCode,
+                creationCode,
                 arg
             ))
         )))));