Re: [PATCH v3] rebase -i: stop checking out the tip of the branch to rebase

> On big repositories, it's a performance penalty: with `rebase -i', the
> user may have to wait before editing the todo list while git is
> extracting the branch silently, and "quiet" rebases will be slower than
> `am'.
>
> Since we already have the oid of the tip of the branch in
> `opts->orig_head', it's useless to switch to this commit.
> ...
>   Before this patch:
>
>     $ time git rebase -m --onto v4.18 463fa44eec2fef50~ 463fa44eec2fef50
>
>     real    0m8,940s
>     user    0m6,830s
>     sys     0m2,121s
>
>   After this patch:
>
>     $ time git rebase -m --onto v4.18 463fa44eec2fef50~ 463fa44eec2fef50
>
>     real    0m1,834s
>     user    0m0,916s
>     sys     0m0,206s
>
> Reported-by: SZEDER Gábor <szeder.dev@gmail.com>
> Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
> ---

> diff --git a/sequencer.c b/sequencer.c
> index b9dbf1adb0..4dc245d7ec 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -3715,20 +3715,6 @@ static int run_git_checkout(struct repository *r, struct replay_opts *opts,
>  	return ret;
>  }
>  
> -int prepare_branch_to_be_rebased(struct repository *r, struct replay_opts *opts,
> -				 const char *commit)
> -{
> -	const char *action;
> -
> -	if (commit && *commit) {
> -		action = reflog_message(opts, "start", "checkout %s", commit);
> -		if (run_git_checkout(r, opts, commit, action))
> -			return error(_("could not checkout %s"), commit);
> -	}
> -
> -	return 0;
> -}
> -
>  static int checkout_onto(struct repository *r, struct replay_opts *opts,
>  			 const char *onto_name, const struct object_id *onto,
>  			 const char *orig_head)
> diff --git a/sequencer.h b/sequencer.h
> index 9f9ae291e3..74f1e2673e 100644
> --- a/sequencer.h
> +++ b/sequencer.h
> @@ -190,9 +190,6 @@ void commit_post_rewrite(struct repository *r,
>  			 const struct commit *current_head,
>  			 const struct object_id *new_head);
>  
> -int prepare_branch_to_be_rebased(struct repository *r, struct replay_opts *opts,
> -				 const char *commit);
> -
>  #define SUMMARY_INITIAL_COMMIT   (1 << 0)
>  #define SUMMARY_SHOW_AUTHOR_DATE (1 << 1)
>  void print_commit_summary(struct repository *repo,