Speed of git branch --contains

Hi everybody,

I'm just looking at some scripts that do a 'git branch --contains $id --remote' for each new commit in a repo, and unfortunately each invokation already takes four minutes.

It feels like git branch does the reachability detection separately for each branch potentially listed. The alternative would be to

- invert the parent map to a child map,
- use that to compute the set of commits that contain $id,
- then use that as predicate whether to show a given branch
  (show iff its head is in the set)

That would speed things up considerably, but what are the chances to see that change in git?

I can do that as well within the script, with the additional benefit that I only need to do the inversion once, but I might instead take a stab at git branch.

- Andreas