Slow file opening on large project

Upon loading a project, opening C++ files can take over 30 seconds. While waiting for the file to load, the application is unresponsive (Windows shades the window white and brings up the "this program is not responding" dialog).

The following details are probably pertinent:

• The project is very large: ~ 15,000 C++ source files, ~ 7,000 other source files ~ 100 include directories.
• After around 10 minutes, some files would open quickly, after leaving the computer idle for over an hour, all files open quickly.
• When a file eventually loads, it is momentarily (for a fraction of a second) shown with incomplete syntax highlighting, before the full syntax highlighting is shown.

Previous behaviour (version 4.0.2) was for the file to load immediately with incomplete syntax highlighting, and the full syntax highlighting (which presumably needs either the internal or clang code model to be computed) would be updated later (possibly within a similar time-frame, but at least the application wasn't locked up in the meantime).