threads / patch / 7388

patchUse diff* with --exit-code in git-am, git-rebase and git-merge-ours

Subject: [PATCH] Use diff* with --exit-code in git-am, git-rebase and git-merge-ours

## tl;dr

3 messages between Mar 25, 2007 and Mar 25, 2007. Diffs are folded; open one to read it.

replies: 2people: 2as markdown or json

Alex Riesen· Mar 25, 2007, 00:56 UTC · lore

This simplifies the shell code, reduces its memory footprint, and speeds things up. The performance improvements should be noticable when git-rebase works on big commits.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
---
 git-am.sh         |   18 +++++++-----------
 git-merge-ours.sh |    2 +-
 git-rebase.sh     |   10 ++++------
 3 files changed, 12 insertions(+), 18 deletions(-)

Show changes to 3 files +12 −18

git-am.sh, git-merge-ours.sh, git-rebase.sh

diff --git a/git-am.sh b/git-am.sh
index 88af8dd..e69ecbf 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -408,12 +408,10 @@ do
 		# trust what the user has in the index file and the
 		# working tree.
 		resolved=
-		changed="$(git-diff-index --cached --name-only HEAD)"
-		if test '' = "$changed"
-		then
+		git-diff-index --quiet --cached HEAD && {
 			echo "No changes - did you forget to use 'git add'?"
 			stop_here_user_resolve $this
-		fi
+		}
 		unmerged=$(git-ls-files -u)
 		if test -n "$unmerged"
 		then
@@ -435,13 +433,11 @@ do
 		then
 		    # Applying the patch to an earlier tree and merging the
 		    # result may have produced the same tree as ours.
-		    changed="$(git-diff-index --cached --name-only HEAD)"
-		    if test '' = "$changed"
-		    then
-			    echo No changes -- Patch already applied.
-			    go_next
-			    continue
-		    fi
+		    git-diff-index --quiet --cached HEAD && {
+			echo No changes -- Patch already applied.
+			go_next
+			continue
+		    }
 		    # clear apply_status -- we have successfully merged.
 		    apply_status=0
 		fi
diff --git a/git-merge-ours.sh b/git-merge-ours.sh
index 4f3d053..2b6a5c0 100755
--- a/git-merge-ours.sh
+++ b/git-merge-ours.sh
@@ -9,6 +9,6 @@
 # because the current index is what we will be committing as the
 # merge result.
 
-test "$(git-diff-index --cached --name-status HEAD)" = "" || exit 2
+git-diff-index --quiet --cached HEAD || exit 2
 
 exit 0
diff --git a/git-rebase.sh b/git-rebase.sh
index aadd580..1d96f32 100755
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -59,7 +59,7 @@ continue_merge () {
 		die "$RESOLVEMSG"
 	fi
 
-	if test -n "`git-diff-index HEAD`"
+	if ! git-diff-index --quiet HEAD
 	then
 		if ! git-commit -C "`cat $dotest/current`"
 		then
@@ -124,13 +124,11 @@ while case "$#" in 0) break ;; esac
 do
 	case "$1" in
 	--continue)
-		diff=$(git-diff-files)
-		case "$diff" in
-		?*)	echo "You must edit all merge conflicts and then"
+		git-diff-files --quiet || {
+			echo "You must edit all merge conflicts and then"
 			echo "mark them as resolved using git update-index"
 			exit 1
-			;;
-		esac
+		}
 		if test -d "$dotest"
 		then
 			prev_head="`cat $dotest/prev_head`"

-- 
1.5.1.rc1.63.g59cc5

Junio C Hamano· Mar 25, 2007, 06:01 UTC · re: Alex Riesen · lore

Re: [PATCH] Use diff* with --exit-code in git-am, git-rebase and git-merge-ours

Alex Riesen <raa.lkml@gmail.com> writes:

> This simplifies the shell code, reduces its memory footprint, and
> speeds things up. The performance improvements should be noticable
> when git-rebase works on big commits.

Thanks.

Unlike some optimizations that tilts the tradeoffs to favor often-used case by penalizing the less often-used case, this change does not penalize any case while optimizing some cases, so there is nothing we are losing. I'll take the patch for this reason.

However, I have a few comments.

Have you run any benchmark? I suspect "and speeds things up" is a gross overstatement. A qualified "SOMETIMES speeds things up" would be a more honest thing to say.

Both of the changes to git-am are definitely good. Under normal usage, we expect that we would see some diff, and the optimization applies to that normal case.

Show 12 quoted lines

> diff --git a/git-merge-ours.sh b/git-merge-ours.sh
> index 4f3d053..2b6a5c0 100755
> --- a/git-merge-ours.sh
> +++ b/git-merge-ours.sh
> @@ -9,6 +9,6 @@
>  # because the current index is what we will be committing as the
>  # merge result.
>  
> -test "$(git-diff-index --cached --name-status HEAD)" = "" || exit 2
> +git-diff-index --quiet --cached HEAD || exit 2
>  
>  exit 0

I think this does not change the performance profile in the real life. When the user uses the command correctly, we expect that index and HEAD to match, and in that case the diff would take the same amount of processing with or without --quiet. The change does not penalize the opposite case, so it is not a wrong thing to do, but this is an optimization to error out early.

The first change to git-rebase optimizes the case to handle "still to be adopted upstream" case ("upstream swallowed our change" case would perform the same as before), so the optimization would be more visible by people with slower upstream and/or people patches of lessor quality that are rejected by upstream often. In other words, the amount of speeding up by this change really depends on the user (there is no slowdown for anybody so that is Ok).

The other optimizes the "erroring out early" uninteresting case.

Alex Riesen· Mar 25, 2007, 09:33 UTC · re: Junio C Hamano · lore

Re: [PATCH] Use diff* with --exit-code in git-am, git-rebase and git-merge-ours

Junio C Hamano, Sun, Mar 25, 2007 08:01:31 +0200:

> However, I have a few comments.
> 
> Have you run any benchmark?  I suspect "and speeds things up" is

I didn't benchmark any of these, so I can't backup the statement with the number but...

> a gross overstatement.  A qualified "SOMETIMES speeds things up"
> would be a more honest thing to say.

it must speed things up, if only for removed shell-side efforts to redirect the output and store it in heap. To overstatement it I should have said: "greatly speeds things up".