The old code didn't use QStringList::removeDuplicates(), because it still needs the QDuplicateTracker for later. It, however, used a loop around erase(it) (or Qt's equivalent for indexed loops), which makes the loop have quadratic complexity, instead of std::remove_if(), which is linear. Fix by using QList::removeIf() instead (which is std::remove_if()). There are more insertion-in-the-middle problems in this function, filed QTBUG-138851 so they're not forgotten. Amends 2c39365aad957aea7ca9c9c861665391edf7ef23, though I'm sure the old code had a similar problem, just buried deeper. This patch won't apply there. Task-number: QTBUG-138851 Pick-to: 6.10 6.9 Change-Id: I5748822bd99dac7cdbd2c1deaec348a82194e994 Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>