[PATCH 09/10] diffcore-rename: limit dir_rename_counts computation to relevant dirs

["Elijah Newren via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Elijah Newren <newren@xxxxxxxxx>

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.

While dirs_removed provides the relevant information for us right now,
we introduce a new info->relevant_source_dirs parameter because future
optimizations will want to change how things are called somewhat.

Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
---
 diffcore-rename.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 1e4a56adde2c..5de4497e04fa 100644
--- a/diffcore-rename.c
+++ b/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;
 };
 
@@ -460,7 +461,13 @@ 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);
 
 		/*
@@ -540,6 +547,9 @@ 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.
-- 
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