index: speedup git_index_append()/git_index_append2()

git_index_find() in index_insert() is useless if replace is not
requested (append). Do not call it in this case.
It speedup git_index_append() *dramatically* on large indexes.

$ cat index_test.c

int main(int argc, char **argv)
{
        git_index *index;
        git_repository *repo;
        git_odb *odb;
        struct git_index_entry entry;
        git_oid tree_oid;
        char tree_hex[41];
        int i;

        git_repository_init(&repo, "/tmp/myrepo", 0);
        odb = git_repository_database(repo);
        git_repository_index(&index, repo);

        memset(&entry, 0, sizeof(entry));
        git_odb_write(&entry.oid, odb, "", 0, GIT_OBJ_BLOB);
        entry.path = "test.file";

        for (i = 0; i < 50000; i++)
                git_index_append2(index, &entry);

        git_tree_create_fromindex(&tree_oid, index);
        git_oid_fmt(tree_hex, &tree_oid);
        tree_hex[40] = '\0';
        printf("tree: %s\n", tree_hex);

        git_index_free(index);
        git_repository_free(repo);

        return 0;
}

Before:
$ time ./index_test
tree: 43f73659c43b651588cc81459d9e25b08721b95d
./index_test  151.19s user 0.05s system 99% cpu 2:31.78 total

After:
$ time ./index_test
tree: 43f73659c43b651588cc81459d9e25b08721b95d
./index_test  0.05s user 0.00s system 94% cpu 0.059 total

About 2573 times speedup on this test :)

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>

src/index.c

@@ -348,6 +348,7 @@ static int index_insert(git_index *index, const git_index_entry *source_entry, i
 	git_index_entry *entry;
 	size_t path_length;
 	int position;
+	git_index_entry **entry_array;
 
 	assert(index && source_entry);
 
@@ -375,27 +376,28 @@ static int index_insert(git_index *index, const git_index_entry *source_entry, i
 	else
 		entry->flags |= GIT_IDXENTRY_NAMEMASK;;
 
+	/*
+	 * replacing is not requested: just insert entry at the end;
+	 * the index is no longer sorted
+	 */
+	if (!replace)
+		return git_vector_insert(&index->entries, entry);
 
 	/* look if an entry with this path already exists */
 	position = git_index_find(index, source_entry->path);
 
-	/* if no entry exists and replace is not set,
+	/*
-	 * add the entry at the end;
+	 * if no entry exists add the entry at the end;
-	 * the index is no longer sorted */
+	 * the index is no longer sorted
-	if (!replace || position == GIT_ENOTFOUND) {
+	 */
-		if (git_vector_insert(&index->entries, entry) < GIT_SUCCESS)
+	if (position == GIT_ENOTFOUND)
-			return GIT_ENOMEM;
+		return git_vector_insert(&index->entries, entry);
 
-	/* if a previous entry exists and replace is set,
+	/* exists, replace it */
-	 * replace it */
+	entry_array = (git_index_entry **) index->entries.contents;
-	} else {
+	free((char *)entry_array[position]->path);
-		git_index_entry **entry_array = (git_index_entry **)index->entries.contents;
+	free(entry_array[position]);
-
+	entry_array[position] = entry;
-		free((char *)entry_array[position]->path);
-		free(entry_array[position]);
-
-		entry_array[position] = entry;
-	}
 
 	return GIT_SUCCESS;
 }