grt: append nodes and edges from removed nets when merging nets

src/ant/src/WireBuilder.cc

@@ -27,7 +27,8 @@ void WireBuilder::makeNetWiresFromGuides()
         = db_net->getWireType() == odb::dbWireType::ROUTED && db_net->getWire();
 
     if (!db_net->isSpecial() && !db_net->isConnectedByAbutment()
-        && !dbNetIsLocal(db_net) && !is_detailed_routed) {
+        && db_net->getTermCount() > 1 && !dbNetIsLocal(db_net)
+        && !is_detailed_routed) {
       makeNetWire(db_net, guide_dimension);
     }
   }
@@ -42,7 +43,8 @@ void WireBuilder::makeNetWiresFromGuides(const std::vector<odb::dbNet*>& nets)
         = db_net->getWireType() == odb::dbWireType::ROUTED && db_net->getWire();
 
     if (!db_net->isSpecial() && !db_net->isConnectedByAbutment()
-        && !dbNetIsLocal(db_net) && !is_detailed_routed) {
+        && db_net->getTermCount() > 1 && !dbNetIsLocal(db_net)
+        && !is_detailed_routed) {
       makeNetWire(db_net, guide_dimension);
     }
   }

src/grt/include/grt/GlobalRouter.h

@@ -303,7 +303,7 @@ class GlobalRouter
   void initRoutingTracks(int max_routing_layer);
   void setCapacities(int min_routing_layer, int max_routing_layer);
   void initNetlist(std::vector<Net*>& nets);
-  bool makeFastrouteNet(Net* net);
+  void makeFastrouteNet(Net* net);
   bool pinPositionsChanged(Net* net);
   bool newPinOnGrid(Net* net, std::multiset<RoutePt>& last_pos);
   std::vector<LayerId> findTransitionLayers();

src/grt/src/GlobalRouter.cpp

@@ -661,7 +661,7 @@ void GlobalRouter::updateDirtyNets(std::vector<Net*>& dirty_nets)
             GRT, 267, "Net {} has disconnected segments.", net->getName());
       }
     }
-    net->setMergedNet(false);
+    net->setIsMergedNet(false);
     net->setDirtyNet(false);
     net->clearLastPinPositions();
   }
@@ -1141,29 +1141,13 @@ bool GlobalRouter::newPinOnGrid(Net* net, std::multiset<RoutePt>& last_pos)
   return false;
 }
 
-bool GlobalRouter::makeFastrouteNet(Net* net)
+void GlobalRouter::makeFastrouteNet(Net* net)
 {
   std::vector<RoutePt> pins_on_grid;
   int root_idx;
   findFastRoutePins(net, pins_on_grid, root_idx);
 
-  if (pins_on_grid.size() <= 1) {
-    return false;
-  }
-
-  // check if net is local in the global routing grid position
-  // the (x,y) pin positions here may be different from the original
-  // (x,y) pin positions because of findFakePinPosition function
-  bool on_grid_local = true;
-  RoutePt position = pins_on_grid[0];
-  for (RoutePt& pin_pos : pins_on_grid) {
-    if (pin_pos.x() != position.x() || pin_pos.y() != position.y()) {
-      on_grid_local = false;
-      break;
-    }
-  }
-
-  if (!on_grid_local) {
+  if (pins_on_grid.size() > 1) {
     bool is_clock = (net->getSignalType() == odb::dbSigType::CLOCK);
     std::vector<int>* edge_cost_per_layer;
     int edge_cost_for_net;
@@ -1197,9 +1181,7 @@ bool GlobalRouter::makeFastrouteNet(Net* net)
         && net->getDbNet() == fastroute_->getDebugNet()) {
       saveSttInputFile(net);
     }
-    return true;
   }
-  return false;
 }
 
 void GlobalRouter::saveSttInputFile(Net* net)
@@ -3573,7 +3555,7 @@ void GlobalRouter::removeNet(odb::dbNet* db_net)
 {
   Net* net = db_net_map_[db_net];
   if (net != nullptr && net->isMergedNet()) {
-    fastroute_->mergeNet(db_net);
+    fastroute_->mergeNet(db_net, net->getMergedNet());
   } else {
     fastroute_->removeNet(db_net);
   }
@@ -4224,11 +4206,16 @@ void GlobalRouter::mergeNetsRouting(odb::dbNet* db_net1, odb::dbNet* db_net2)
 {
   Net* net1 = db_net_map_[db_net1];
   Net* net2 = db_net_map_[db_net2];
-  // Do not merge the routing if the survivor net is already dirty
-  if (!net1->isDirtyNet()) {
+  // Do not merge the routing if the survivor net is already dirty.
+  // Also, do not merge if the survivor net is a local net, since it doesn't
+  // have routes inside FastRouteCore.
+  // TODO: properly handle local nets when merging global routes.
+  if (!net1->isDirtyNet() && !net1->isLocal()) {
     connectRouting(db_net1, db_net2);
-    net1->setMergedNet(true);
-    net2->setMergedNet(true);
+    net1->setIsMergedNet(true);
+    net1->setMergedNet(db_net2);
+    net2->setIsMergedNet(true);
+    net2->setMergedNet(db_net1);
   }
 }
 

src/grt/src/Net.cpp

@@ -18,7 +18,8 @@ Net::Net(odb::dbNet* net, bool has_wires)
     : net_(net),
       slack_(0),
       has_wires_(has_wires),
-      merged_net_(false),
+      merged_net_(nullptr),
+      is_merged_net_(false),
       is_dirty_net_(false)
 {
 }

src/grt/src/Net.h

@@ -50,8 +50,10 @@ class Net
   {
     return last_pin_positions_;
   }
-  void setMergedNet(bool merged_net) { merged_net_ = merged_net; }
-  bool isMergedNet() const { return merged_net_; }
+  void setMergedNet(odb::dbNet* merged_net) { merged_net_ = merged_net; }
+  odb::dbNet* getMergedNet() const { return merged_net_; }
+  void setIsMergedNet(bool merged_net) { is_merged_net_ = merged_net; }
+  bool isMergedNet() const { return is_merged_net_; }
   void setDirtyNet(bool is_dirty_net) { is_dirty_net_ = is_dirty_net; }
   bool isDirtyNet() const { return is_dirty_net_; }
 
@@ -64,7 +66,8 @@ class Net
   bool has_wires_;
   std::vector<SegmentIndex> parent_segment_indices_;
   std::multiset<RoutePt> last_pin_positions_;
-  bool merged_net_;
+  odb::dbNet* merged_net_;
+  bool is_merged_net_;
   bool is_dirty_net_;
 };
 

src/grt/src/fastroute/include/FastRoute.h

@@ -109,7 +109,7 @@ class FastRouteCore
                 std::vector<int>* edge_cost_per_layer);
   void deleteNet(odb::dbNet* db_net);
   void removeNet(odb::dbNet* db_net);
-  void mergeNet(odb::dbNet* db_net);
+  void mergeNet(odb::dbNet* removed_net, odb::dbNet* preserved_net);
   void clearNetRoute(odb::dbNet* db_net);
   void clearNetsToRoute() { net_ids_.clear(); }
   void initEdges();

src/grt/src/fastroute/src/FastRoute.cpp

@@ -291,13 +291,29 @@ void FastRouteCore::removeNet(odb::dbNet* db_net)
   }
 }
 
-void FastRouteCore::mergeNet(odb::dbNet* db_net)
+void FastRouteCore::mergeNet(odb::dbNet* removed_net, odb::dbNet* preserved_net)
 {
-  if (db_net_id_map_.find(db_net) != db_net_id_map_.end()) {
-    const int net_id = db_net_id_map_[db_net];
-    sttrees_[net_id].nodes.clear();
-    sttrees_[net_id].edges.clear();
-    deleteNet(db_net);
+  if (db_net_id_map_.find(removed_net) != db_net_id_map_.end()) {
+    const int removed_net_id = db_net_id_map_[removed_net];
+    auto& removed_nodes = sttrees_[removed_net_id].nodes;
+    auto& removed_edges = sttrees_[removed_net_id].edges;
+
+    if (db_net_id_map_.find(preserved_net) != db_net_id_map_.end()) {
+      const int preserved_net_id = db_net_id_map_[preserved_net];
+      sttrees_[preserved_net_id].num_terminals
+          += sttrees_[removed_net_id].num_terminals;
+      auto& preserved_nodes = sttrees_[preserved_net_id].nodes;
+      auto& preserved_edges = sttrees_[preserved_net_id].edges;
+
+      preserved_nodes.insert(
+          preserved_nodes.end(), removed_nodes.begin(), removed_nodes.end());
+      preserved_edges.insert(
+          preserved_edges.end(), removed_edges.begin(), removed_edges.end());
+    }
+
+    removed_nodes.clear();
+    removed_edges.clear();
+    deleteNet(removed_net);
   }
 }