MinGW build of Qt 5.0.1 (from qt-project.org) much worse performance when handling QByteArrays and I/O (and probably everything in QtCore) then Qt 4.8.4. In my application that loads a text-based data file line-by-line, splits it in fields, converts them to other data types and saves everything to a file slowdown is 2-3 times depending on what kind of processing is done. I'm attaching a simple benchmark that demonstrates the problem. On my system I have the following results:
That's 2.9 times slowdown. I guess it is related to use of SJLJ exceptions with the new toolchain. I cannot reproduce the slowdown in Linux. Using CONFIG+=exceptions_off also does not significantly improve performance.
It would be good to have MinGW build without such large performance regression.