When a non-QString-backed mode (via the (QChar*, int) ctor) was added for Qt 4.5, the author forgot to adjust the setCaseSensitivity() function. It still uses q_pattern instead of (p.uc, p.len) as the pattern for which to create the skip-table. Since there is no setPattern() overload for this mode, the correctness of the matcher is not harmed by this, but its performance degrades to that of a linear scan: the skip-table, being filled from an empty pattern, will be all-zeros, sending bm_find() into the 'possible match' case at every character. Since matching is still correct, but slow, it's not possible to write a test for this. I did, however, leave my attempts in the auto-test, for when we add QStringView overloads of setPattern() which will then be able to expose the bug. Change-Id: I7b803e8624b0352a0a974900affbbfc0c260d93b Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com> Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>