CppEditor hangs QtCreator while find reference symbols

To be clearly, when press Ctrl and move mouse, QtCreator will hangs for a long time.

Most of the time I'm trying double click a word (variable, function etc), and then press Ctrl + C to copy the codes, QtCreator will hangs for a while.
As I debug QtCreator, most of the time spends inside TypeOfExpression::reference at src/plugins/cppeditor/cppfollowsymbolundercursor.cpp +696.
Inserted a timer for debugging, I can see every call costs 480 ~ 600 ms, do a Ctrl and move mouse cause many calls to update link! (plus all turns to many seconds)

This bug only occures when you open a big project (Qt5 isn't that big, as I tested with it). If I'm right, many versions (2.x or qt4 serials ?) ago I don't have this issue.

P.S. I also tested the official package qt-creator-opensource-linux-x86_64-3.4.2.run, just the same.