Re: [PATCH 1/2] completion: improve ls-files filter performance

[Junio C Hamano <gitster@pobox.com>]

Clemens Buchacher <drizzd@gmx.net> writes:

> From the output of ls-files, we remove all but the leftmost path
> component and then we eliminate duplicates. We do this in a while loop,
> which is a performance bottleneck when the number of iterations is large
> (e.g. for 60000 files in linux.git).
>
> $ COMP_WORDS=(git status -- ar) COMP_CWORD=3; time _git
>
> real    0m11.876s
> user    0m4.685s
> sys     0m6.808s
>
> Using an equivalent sed script improves performance significantly:
>
> $ COMP_WORDS=(git status -- ar) COMP_CWORD=3; time _git
>
> real    0m1.372s
> user    0m0.263s
> sys     0m0.167s
>
> The measurements were done with mingw64 bash, which is used by Git for
> Windows.
>
> Signed-off-by: Clemens Buchacher <drizzd@gmx.net>
> ---
>  contrib/completion/git-completion.bash | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
> index 6da95b8..e3ddf27 100644
> --- a/contrib/completion/git-completion.bash
> +++ b/contrib/completion/git-completion.bash
> @@ -384,12 +384,7 @@ __git_index_files ()
>  	local root="${2-.}" file
>  
>  	__git_ls_files_helper "$root" "$1" |
> -	while read -r file; do
> -		case "$file" in
> -		?*/*) echo "${file%%/*}" ;;
> -		*) echo "$file" ;;
> -		esac
> -	done | sort | uniq
> +	sed -e '/^\//! s#/.*##' | sort | uniq

Micronit: perhaps lose SP after '!'?

cf. http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sed.html

"""A function can be preceded by a '!' character, in which case the
function shall be applied if the addresses do not select the pattern
space. Zero or more <blank> characters shall be accepted before the
'!' character. It is unspecified whether <blank> characters can
follow the '!' character, and conforming applications shall not
follow the '!' character with <blank> characters."""


>  }
>  
>  # Lists branches from the local repository.