diff --git a/include/sta/Search.hh b/include/sta/Search.hh
index d54a8a5b..40ddc542 100644
--- a/include/sta/Search.hh
+++ b/include/sta/Search.hh
@@ -356,7 +356,8 @@ public:
 
   TagGroup *tagGroup(const Vertex *vertex) const;
   TagGroup *tagGroup(TagGroupIndex index) const;
-  void reportArrivals(Vertex *vertex) const;
+  void reportArrivals(Vertex *vertex,
+		      bool report_tag_index) const;
   Slack wnsSlack(Vertex *vertex,
 		 PathAPIndex path_ap_index);
   void levelsChangedBefore();
@@ -410,6 +411,7 @@ public:
                         TagGroupIndex tag_index);
   void checkPrevPaths() const;
   void deletePaths(Vertex *vertex);
+  void deleteTagGroup(TagGroup *group);
 
 protected:
   void init(StaState *sta);
@@ -645,6 +647,7 @@ protected:
   // Capacity of tag_groups_.
   TagGroupIndex tag_group_capacity_;
   std::mutex tag_group_lock_;
+  std::mutex tag_group_ref_count_lock_;
   // Latches data outputs to queue on the next search pass.
   VertexSet *pending_latch_outputs_;
   std::mutex pending_latch_outputs_lock_;
diff --git a/search/Search.cc b/search/Search.cc
index 8677dab6..2023daca 100644
--- a/search/Search.cc
+++ b/search/Search.cc
@@ -554,15 +554,20 @@ Search::deleteFilterTagGroups()
   for (TagGroupIndex i = 0; i < tag_group_next_; i++) {
     TagGroup *group = tag_groups_[i];
     if (group
-	&& group->hasFilterTag()) {
-      tag_group_set_->erase(group);
-      tag_groups_[group->index()] = nullptr;
-      tag_group_free_indices_.push_back(i);
-      delete group;
-    }
+	&& group->hasFilterTag())
+      deleteTagGroup(group);
   }
 }
 
+void
+Search::deleteTagGroup(TagGroup *group)
+{
+  tag_group_set_->erase(group);
+  tag_groups_[group->index()] = nullptr;
+  tag_group_free_indices_.push_back(group->index());
+  delete group;
+}
+
 void
 Search::deleteFilterTags()
 {
@@ -2777,6 +2782,15 @@ Search::setVertexArrivals(Vertex *vertex,
         filtered_arrivals_->insert(vertex);
       }
     }
+    if (tag_group != prev_tag_group) {
+      LockGuard lock(tag_group_ref_count_lock_);
+      tag_group->incrRefCount();
+      if (prev_tag_group) {
+	prev_tag_group->decrRefCount();
+	if (prev_tag_group->refCount() == 0)
+	  deleteTagGroup(prev_tag_group);
+      }
+    }
   }
 }
 
@@ -2819,12 +2833,14 @@ ReportPathLess::operator()(const Path *path1,
 }
 
 void
-Search::reportArrivals(Vertex *vertex) const
+Search::reportArrivals(Vertex *vertex,
+		       bool report_tag_index) const
 {
   report_->reportLine("Vertex %s", vertex->to_string(this).c_str());
   TagGroup *tag_group = tagGroup(vertex);
   if (tag_group) {
-    report_->reportLine("Group %u", tag_group->index());
+    if (report_tag_index)
+      report_->reportLine("Group %u", tag_group->index());
     std::vector<const Path*> paths;
     VertexPathIterator path_iter(vertex, this);
     while (path_iter.hasNext()) {
@@ -2859,7 +2875,7 @@ Search::reportArrivals(Vertex *vertex) const
                           path_ap->pathMinMax()->to_string().c_str(),
                           delayAsString(path->arrival(), this),
                           req,
-                          tag->to_string(true, false, this).c_str(),
+                          tag->to_string(report_tag_index, false, this).c_str(),
                           prev_str.c_str());
     }
   }
diff --git a/search/Search.i b/search/Search.i
index 73f4761a..76338830 100644
--- a/search/Search.i
+++ b/search/Search.i
@@ -264,9 +264,10 @@ report_tag_groups()
 }
 
 void
-report_tag_arrivals_cmd(Vertex *vertex)
+report_tag_arrivals_cmd(Vertex *vertex,
+			bool report_tag_index)
 {
-  Sta::sta()->search()->reportArrivals(vertex);
+  Sta::sta()->search()->reportArrivals(vertex, report_tag_index);
 }
 
 void
diff --git a/search/Tag.cc b/search/Tag.cc
index d4e36bae..80578548 100644
--- a/search/Tag.cc
+++ b/search/Tag.cc
@@ -355,7 +355,7 @@ tagCmp(const Tag *tag1,
   return tagStateCmp(tag1, tag2);
 }
 
-int
+bool
 tagEqual(const Tag *tag1,
 	 const Tag *tag2)
 {
diff --git a/search/Tag.hh b/search/Tag.hh
index 3fa91de2..d0e44506 100644
--- a/search/Tag.hh
+++ b/search/Tag.hh
@@ -140,6 +140,9 @@ public:
 		  const Tag *tag2) const;
 };
 
+bool
+tagEqual(const Tag *tag1,
+	 const Tag *tag2);
 int
 tagCmp(const Tag *tag1,
        const Tag *tag2,
diff --git a/search/TagGroup.cc b/search/TagGroup.cc
index f060463b..5a79f7de 100644
--- a/search/TagGroup.cc
+++ b/search/TagGroup.cc
@@ -44,6 +44,7 @@ TagGroup::TagGroup(TagGroupIndex index,
 		   bool has_loop_tag) :
   path_index_map_(path_index_map),
   hash_(pathIndexMapHash(path_index_map)),
+  ref_count_(0),
   index_(index),
   has_clk_tag_(has_clk_tag),
   has_genclk_src_tag_(has_genclk_src_tag),
@@ -56,6 +57,7 @@ TagGroup::TagGroup(TagGroupIndex index,
 TagGroup::TagGroup(TagGroupBldr *tag_bldr) :
   path_index_map_(&tag_bldr->pathIndexMap()),
   hash_(pathIndexMapHash(path_index_map_)),
+  ref_count_(0),
   own_path_map_(false)
 {
 }
@@ -66,6 +68,18 @@ TagGroup::~TagGroup()
     delete path_index_map_;
 }
 
+void
+TagGroup::incrRefCount()
+{
+  ref_count_++;
+}
+
+void
+TagGroup::decrRefCount()
+{
+  ref_count_--;
+}
+
 size_t
 TagGroup::pathIndexMapHash(PathIndexMap *path_index_map)
 {
diff --git a/search/TagGroup.hh b/search/TagGroup.hh
index a54f9045..74b073ab 100644
--- a/search/TagGroup.hh
+++ b/search/TagGroup.hh
@@ -65,6 +65,9 @@ public:
   size_t pathIndex(Tag *tag) const;
   PathIndexMap *pathIndexMap() const { return path_index_map_; }
   bool hasTag(Tag *tag) const;
+  void incrRefCount();
+  void decrRefCount();
+  int refCount() const { return ref_count_; }
 
 protected:
   static size_t pathIndexMapHash(PathIndexMap *path_index_map);
@@ -72,6 +75,7 @@ protected:
   // tag -> path index
   PathIndexMap *path_index_map_;
   size_t hash_;
+  int ref_count_;
   unsigned int index_:tag_group_index_bits;
   bool has_clk_tag_:1;
   bool has_genclk_src_tag_:1;