[PATCH] subtree: performance improvement for finding unexpected parent commits

[Roger Strain <rstrain@swri.org>]

After testing a previous patch at larger scale, a performance issue was
detected when using git show to locate parent revisions, with a single
run of the git show command taking 2 seconds or longer in a complex repo.
When the command is required tens or hundreds of times in a run of the
script, the additional wait time is unaccepatable. Replacing the command
with git rev-parse resulted in significantly increased performance, with
the command in question returning instantly.

Signed-off-by: Roger Strain <rstrain@swri.org>
Thanks-to: Junio C Hamano <gitster@pobox.com>
---
 contrib/subtree/git-subtree.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index 1c157dbd9..147201dc6 100755
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
@@ -633,7 +633,7 @@ process_split_commit () {
 	else
 		# processing commit without normal parent information;
 		# fetch from repo
-		parents=$(git show -s --pretty=%P "$rev")
+		parents=$(git rev-parse "$rev^@")
 		extracount=$(($extracount + 1))
 	fi
 
-- 
2.19.1