diffcore-rename: limit dir_rename_counts computation to relevant dirs

We are using dir_rename_counts to count the number of other directories
that files within a directory moved to.  We only need this information
for directories that disappeared, though, so we can return early from
update_dir_rename_counts() for other paths.

If dirs_removed is passed to diffcore_rename_extended(), then it
provides the relevant bits of information for us to limit this counting
to relevant dirs.  If dirs_removed is not passed, we would need to
compute some replacement in order to do this limiting.  Introduce a new
info->relevant_source_dirs variable for this purpose, even though at
this stage we will only set it to dirs_removed for simplicity.

Reviewed-by: Derrick Stolee <[email protected]>
Signed-off-by: Elijah Newren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: newren

diffcore-rename.c

@@ -371,6 +371,7 @@ struct dir_rename_info {
 	struct strintmap idx_map;
 	struct strmap dir_rename_guess;
 	struct strmap *dir_rename_count;
+	struct strset *relevant_source_dirs;
 	unsigned setup;
 };
 
@@ -442,7 +443,13 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
 		return;
 
 	while (1) {
+		/* Get old_dir, skip if its directory isn't relevant. */
 		dirname_munge(old_dir);
+		if (info->relevant_source_dirs &&
+		    !strset_contains(info->relevant_source_dirs, old_dir))
+			break;
+
+		/* Get new_dir */
 		dirname_munge(new_dir);
 
 		/*
@@ -521,6 +528,9 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 	strintmap_init_with_options(&info->idx_map, -1, NULL, 0);
 	strmap_init_with_options(&info->dir_rename_guess, NULL, 0);
 
+	/* Setup info->relevant_source_dirs */
+	info->relevant_source_dirs = dirs_removed;
+
 	/*
 	 * Loop setting up both info->idx_map, and doing setup of
 	 * info->dir_rename_count.