optimized checkout+rebase?

[Ralf Wildenhues <Ralf.Wildenhues@gmx.de>]

Hello,

this is a common work pattern:

  git checkout master
  git pull
  for branch in $my_topic_branches; do
    git checkout $branch
    git rebase master
    # occasional fixups here...
  done

Now, it looks to me that one of the first operations of rebase just
undoes part of the work that the checkout of the branch did.  Well,
"undoes" is the wrong word, what I mean is that it looks like work
may be saved by combining the two checkout and the rewinding step.

Has this optimization already been implemented in git by some command
I've overlooked, and if no, do you agree that there is some optimization
possible?

Thanks,
Ralf