Re: [PATCH 3/2] Optimize the two-way merge of git-read-tree too

[Linus Torvalds <torvalds@linux-foundation.org>]

On Fri, 10 Aug 2007, Linus Torvalds wrote:
> 
> This trivially optimizes the two-way merge case of git-read-tree too, 
> which affects switching branches.

Side note, if this wasn't obvious: this series of three patches (four, if 
you count the one in this email) obviates the need for Junio's hacky fix 
from yesterday that removed the "-i -m" flags from "git read-tree" in 
git-commit.sh, and made builtin-read-tree sometimes use the "read_tree()" 
function.

Now "unpack_trees()" is just fast enough that we don't need to avoid it 
(although it's probably still a good idea to eventually convert it to use 
the traverse_trees() infrastructure some day - just to avoid having 
extraneous tree traversal functions).

And as mentioned, the three-way case *should* be as trivial as the 
following. It passes all the tests, and I verified that a conflicting 
merge in the 100,000 file horror-case merged correctly (with the conflict 
markers) in 0.687 seconds with this, so it works, but I'm lazy and 
somebody else should double-check it.

(Again - *without* this patch, the merge took 8.355 seconds, so this patch 
really does make a huge difference for merge performance with lots and 
lots of files, and we're not talking percentages, we're talking 
orders-of-magnitude differences!)

		Linus

---
 unpack-trees.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 810816e..ccfeb6e 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -667,7 +667,6 @@ int threeway_merge(struct cache_entry **stages,
 	int no_anc_exists = 1;
 	int i;
 
-	remove_entry(remove);		
 	for (i = 1; i < o->head_idx; i++) {
 		if (!stages[i] || stages[i] == o->df_conflict_entry)
 			any_anc_missing = 1;
@@ -730,8 +729,10 @@ int threeway_merge(struct cache_entry **stages,
 	}
 
 	/* #1 */
-	if (!head && !remote && any_anc_missing)
+	if (!head && !remote && any_anc_missing) {
+		remove_entry(remove);
 		return 0;
+	}
 
 	/* Under the new "aggressive" rule, we resolve mostly trivial
 	 * cases that we historically had git-merge-one-file resolve.
@@ -763,6 +764,7 @@ int threeway_merge(struct cache_entry **stages,
 		if ((head_deleted && remote_deleted) ||
 		    (head_deleted && remote && remote_match) ||
 		    (remote_deleted && head && head_match)) {
+			remove_entry(remove);
 			if (index)
 				return deleted_entry(index, index, o);
 			else if (ce && !head_deleted)
@@ -785,6 +787,7 @@ int threeway_merge(struct cache_entry **stages,
 		verify_uptodate(index, o);
 	}
 
+	remove_entry(remove);
 	o->nontrivial_merge = 1;
 
 	/* #2, #3, #4, #6, #7, #9, #10, #11. */