The patch no longer applies to source code, due to other recent GiST changes. Parts of it were modifying functions which no longer exist. I picked out the bits which still seemed relevant, and a patch with that is attached. The improvement in REINDEX time is now only about 0.25% on my machine at home, which is small enough that it could easily be from code shifting around. (Or such shifts might be hiding a larger actual savings.) In any event, this patch doesn't seem to be justified as a performance patch, based on my benchmarks today.
On the other hand, this patch leaves the code a few lines shorter and eliminates some unnecessary Datum wrapping, PG_FUNCTION_ARGS parameters on a static function, and allows that function to be called directly rather than using DirectFunctionCall2(). I find the resulting code a little cleaner and easier to read. I would prefer to see it applied on that basis, personally.
Since the author is a committer, and this is a pretty minor code style patch at this point, I'll mark it "Ready for Committer" and leave it to Heikki to decide what to do with it.