diff --git a/diffcore-rename.c b/diffcore-rename.c
index 7cc24592617e..dfbe65c917e9 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -568,7 +568,8 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
 static void initialize_dir_rename_info(struct dir_rename_info *info,
 				       struct strintmap *relevant_sources,
 				       struct strintmap *dirs_removed,
-				       struct strmap *dir_rename_count)
+				       struct strmap *dir_rename_count,
+				       struct strmap *cached_pairs)
 {
 	struct hashmap_iter iter;
 	struct strmap_entry *entry;
@@ -633,6 +634,17 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 					 rename_dst[i].p->two->path);
 	}
 
+	/* Add cached_pairs to counts */
+	strmap_for_each_entry(cached_pairs, &iter, entry) {
+		const char *old_name = entry->key;
+		const char *new_name = entry->value;
+		if (!new_name)
+			/* known delete; ignore it */
+			continue;
+
+		update_dir_rename_counts(info, dirs_removed, old_name, new_name);
+	}
+
 	/*
 	 * Now we collapse
 	 *    dir_rename_count: old_directory -> {new_directory -> count}
@@ -1247,7 +1259,8 @@ static void handle_early_known_dir_renames(struct dir_rename_info *info,
 void diffcore_rename_extended(struct diff_options *options,
 			      struct strintmap *relevant_sources,
 			      struct strintmap *dirs_removed,
-			      struct strmap *dir_rename_count)
+			      struct strmap *dir_rename_count,
+			      struct strmap *cached_pairs)
 {
 	int detect_rename = options->detect_rename;
 	int minimum_score = options->rename_score;
@@ -1363,7 +1376,8 @@ void diffcore_rename_extended(struct diff_options *options,
 		/* Preparation for basename-driven matching. */
 		trace2_region_enter("diff", "dir rename setup", options->repo);
 		initialize_dir_rename_info(&info, relevant_sources,
-					   dirs_removed, dir_rename_count);
+					   dirs_removed, dir_rename_count,
+					   cached_pairs);
 		trace2_region_leave("diff", "dir rename setup", options->repo);
 
 		/* Utilize file basenames to quickly find renames. */
@@ -1561,5 +1575,5 @@ void diffcore_rename_extended(struct diff_options *options,
 
 void diffcore_rename(struct diff_options *options)
 {
-	diffcore_rename_extended(options, NULL, NULL, NULL);
+	diffcore_rename_extended(options, NULL, NULL, NULL, NULL);
 }
diff --git a/diffcore.h b/diffcore.h
index cf8d4cb8617d..de01e64becaf 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -181,7 +181,8 @@ void diffcore_rename(struct diff_options *);
 void diffcore_rename_extended(struct diff_options *options,
 			      struct strintmap *relevant_sources,
 			      struct strintmap *dirs_removed,
-			      struct strmap *dir_rename_count);
+			      struct strmap *dir_rename_count,
+			      struct strmap *cached_pairs);
 void diffcore_merge_broken(void);
 void diffcore_pickaxe(struct diff_options *);
 void diffcore_order(const char *orderfile);
diff --git a/merge-ort.c b/merge-ort.c
index 8d0353ffbca2..719222aa4364 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -752,15 +752,48 @@ static void add_pair(struct merge_options *opt,
 	struct rename_info *renames = &opt->priv->renames;
 	int names_idx = is_add ? side : 0;
 
-	if (!is_add) {
+	if (is_add) {
+		if (strset_contains(&renames->cached_target_names[side],
+				    pathname))
+			return;
+	} else {
 		unsigned content_relevant = (match_mask == 0);
 		unsigned location_relevant = (dir_rename_mask == 0x07);
 
+		/*
+		 * If pathname is found in cached_irrelevant[side] due to
+		 * previous pick but for this commit content is relevant,
+		 * then we need to remove it from cached_irrelevant.
+		 */
+		if (content_relevant)
+			/* strset_remove is no-op if strset doesn't have key */
+			strset_remove(&renames->cached_irrelevant[side],
+				      pathname);
+
+		/*
+		 * We do not need to re-detect renames for paths that we already
+		 * know the pairing, i.e. for cached_pairs (or
+		 * cached_irrelevant).  However, handle_deferred_entries() needs
+		 * to loop over the union of keys from relevant_sources[side] and
+		 * cached_pairs[side], so for simplicity we set relevant_sources
+		 * for all the cached_pairs too and then strip them back out in
+		 * prune_cached_from_relevant() at the beginning of
+		 * detect_regular_renames().
+		 */
 		if (content_relevant || location_relevant) {
 			/* content_relevant trumps location_relevant */
 			strintmap_set(&renames->relevant_sources[side], pathname,
 				      content_relevant ? RELEVANT_CONTENT : RELEVANT_LOCATION);
 		}
+
+		/*
+		 * Avoid creating pair if we've already cached rename results.
+		 * Note that we do this after setting relevant_sources[side]
+		 * as noted in the comment above.
+		 */
+		if (strmap_contains(&renames->cached_pairs[side], pathname) ||
+		    strset_contains(&renames->cached_irrelevant[side], pathname))
+			return;
 	}
 
 	one = alloc_filespec(pathname);
@@ -2336,7 +2369,9 @@ static inline int possible_side_renames(struct rename_info *renames,
 static inline int possible_renames(struct rename_info *renames)
 {
 	return possible_side_renames(renames, 1) ||
-	       possible_side_renames(renames, 2);
+	       possible_side_renames(renames, 2) ||
+	       !strmap_empty(&renames->cached_pairs[1]) ||
+	       !strmap_empty(&renames->cached_pairs[2]);
 }
 
 static void resolve_diffpair_statuses(struct diff_queue_struct *q)
@@ -2360,7 +2395,6 @@ static void resolve_diffpair_statuses(struct diff_queue_struct *q)
 	}
 }
 
-MAYBE_UNUSED
 static void prune_cached_from_relevant(struct rename_info *renames,
 				       unsigned side)
 {
@@ -2380,7 +2414,6 @@ static void prune_cached_from_relevant(struct rename_info *renames,
 	}
 }
 
-MAYBE_UNUSED
 static void use_cached_pairs(struct merge_options *opt,
 			     struct strmap *cached_pairs,
 			     struct diff_queue_struct *pairs)
@@ -2463,6 +2496,7 @@ static void detect_regular_renames(struct merge_options *opt,
 	struct diff_options diff_opts;
 	struct rename_info *renames = &opt->priv->renames;
 
+	prune_cached_from_relevant(renames, side_index);
 	if (!possible_side_renames(renames, side_index)) {
 		/*
 		 * No rename detection needed for this side, but we still need
@@ -2473,6 +2507,7 @@ static void detect_regular_renames(struct merge_options *opt,
 		return;
 	}
 
+	partial_clear_dir_rename_count(&renames->dir_rename_count[side_index]);
 	repo_diff_setup(opt->repo, &diff_opts);
 	diff_opts.flags.recursive = 1;
 	diff_opts.flags.rename_empty = 0;
@@ -2490,7 +2525,8 @@ static void detect_regular_renames(struct merge_options *opt,
 	diffcore_rename_extended(&diff_opts,
 				 &renames->relevant_sources[side_index],
 				 &renames->dirs_removed[side_index],
-				 &renames->dir_rename_count[side_index]);
+				 &renames->dir_rename_count[side_index],
+				 &renames->cached_pairs[side_index]);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);
 	resolve_diffpair_statuses(&diff_queued_diff);
 
@@ -2597,6 +2633,8 @@ static int detect_and_process_renames(struct merge_options *opt,
 	trace2_region_enter("merge", "regular renames", opt->repo);
 	detect_regular_renames(opt, MERGE_SIDE1);
 	detect_regular_renames(opt, MERGE_SIDE2);
+	use_cached_pairs(opt, &renames->cached_pairs[1], &renames->pairs[1]);
+	use_cached_pairs(opt, &renames->cached_pairs[2], &renames->pairs[2]);
 	trace2_region_leave("merge", "regular renames", opt->repo);
 
 	trace2_region_enter("merge", "directory renames", opt->repo);
