merge: Use `git_index__fill` to populate the indexvmg/index-fill

Instead of calling `git_index_add` in a loop, use the new
`git_index_fill` internal API to fill the index with the initial staged
entries.

The new `fill` helper assumes that all the entries will be unique and
valid, so it can append them at the end of the entries vector and only
sort it once at the end. It performs no validation checks.

This prevents the quadratic behavior caused by having to sort the
entries list once after every insertion.

3 files changed, 41 insertions, 5 deletions

diff --git a/src/index.c b/src/index.c
index 26cd83851..60e4d443c 100644
--- a/src/index.c
+++ b/src/index.c
@@ -1542,6 +1542,43 @@ int git_index_remove_bypath(git_index *index, const char *path)
 	return 0;
 }
 
+int git_index__fill(git_index *index, const git_vector *source_entries)
+{
+	const git_index_entry *source_entry = NULL;
+	size_t i;
+	int ret = 0;
+
+	assert(index);
+
+	if (git_mutex_lock(&index->lock) < 0) {
+		giterr_set(GITERR_OS, "Unable to acquire index lock");
+		return -1;
+	}
+
+	git_vector_foreach(source_entries, i, source_entry) {
+		git_index_entry *entry = NULL;
+
+		if ((ret = index_entry_dup(&entry, index, source_entry)) < 0)
+			break;
+
+		entry->flags_extended |= GIT_IDXENTRY_UPTODATE;
+
+		ret = git_vector_insert(&index->entries, entry);
+		if (ret < 0)
+			break;
+
+		INSERT_IN_MAP(index, entry, ret);
+		if (ret < 0)
+			break;
+	}
+
+	if (!ret)
+		git_vector_sort(&index->entries);
+
+	git_mutex_unlock(&index->lock);
+	return ret;
+}
+
 
 int git_index_add(git_index *index, const git_index_entry *source_entry)
 {
diff --git a/src/index.h b/src/index.h
index 9baf976ee..0909da889 100644
--- a/src/index.h
+++ b/src/index.h
@@ -113,6 +113,8 @@ GIT_INLINE(bool) git_index_entry_newer_than_index(
 extern int git_index__find_pos(
 	size_t *at_pos, git_index *index, const char *path, size_t path_len, int stage);
 
+extern int git_index__fill(git_index *index, const git_vector *source_entries);
+
 extern void git_index__set_ignore_case(git_index *index, bool ignore_case);
 
 extern unsigned int git_index__create_mode(unsigned int mode);
diff --git a/src/merge.c b/src/merge.c
index 9eb3b0904..61ff93c19 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -1739,7 +1739,6 @@ static int index_from_diff_list(git_index **out,
 {
 	git_index *index;
 	size_t i;
-	git_index_entry *entry;
 	git_merge_diff *conflict;
 	int error = 0;
 
@@ -1748,10 +1747,8 @@ static int index_from_diff_list(git_index **out,
 	if ((error = git_index_new(&index)) < 0)
 		return error;
 
-	git_vector_foreach(&diff_list->staged, i, entry) {
-		if ((error = git_index_add(index, entry)) < 0)
-			goto on_error;
-	}
+	if ((error = git_index__fill(index, &diff_list->staged)) < 0)
+		goto on_error;
 
 	git_vector_foreach(&diff_list->conflicts, i, conflict) {
 		const git_index_entry *ancestor =