Howto get repository up2date after pull with touching as less as possible files in the working directory

Hello alltogether, at the moment I ensrure that there are no dirty files before the pull and do a

	git-read-tree HEAD
	git-checkout -a -f
	git-update-cache --refresh

this is suboptimal because all the files in my working directory get a new timestamp and if I call make everything is recompiled (ccache helps, but is not the solution to this problem).

So what is the right way to touch *only* the files which are dirty. Are there any shortcuts? Or should I call 'git dirty' pipe that to git-checkout -f?

	Thomas