Creator gets unresponsive when inserting new lines in huge C++ files

Steps to reproduce:

1. Open huge file (I used sqlite3.c from <creator src>/src/libs/3rdparty/sqlite)
2. Make sure cursor is positioned at the beginning of the file
3. Insert a new line by pressing enter

After that Qt Creator freezes for several minutes here.

I put a scoped pointer into ClangFormatForwardingIndenter::indent and it also takes around 200ms for big files like the texteditor.cpp

All measurements and tests have been done with a release version of Qt Creator and ClangFormat. It gets notably worse when using debug builds of those.

This is not reproducible if Qt Creator is started without the ClangFormat plugin.