Optimize the three-way merge of git-read-tree

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 [jc: followed all three-way merge
codepaths and verified it removes when it should].

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!

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).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/unpack-trees.c b/unpack-trees.c
index fda7729f1d0e7eb85f449e41800a74278bc48254..ccfeb6e245f32d88170ae51f0367ee15aa950a37 100644 (file)
--- 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. */