performance: normalize self._root, avoid calling os.path.join() in dirstate In dirstate, self._join() might get called a lot. Instead of calling it we create self._rootdir and we then only need to append the filename.

performance: do not stat() things when not required Ignore unknown files if we don't need them (eg in hg diff). It slows things down a little bit for big trees (kernel repo), since _join() is called for each file instead of for each directory. fix issue567