in_merge_bases() is too expensive for recent "pu" update

I just did a "git fetch". It took 19 seconds (measured with
gettimeofday) to finish in_merge_bases() in update_local_ref() in
fetch.c, just to print this line

 + a4f2db3...b95a282 pu         -> origin/pu  (forced update)

It's partly my fault because I'm on gcc -O0. But should it not take
that much time for one line? As a grumpy user, I'd be perfectly ok
with git saying "probably forced update, check it yourself" if the
spent time exceeds half a second. On the same token, if diffstat takes
too long for git-pull, then perhaps just stop and print "do it
yourself".
-- 
Duy