mpl: evaluate connection between clusters based on connections' ratio

src/mpl/README.md

@@ -26,7 +26,6 @@ rtl_macro_placer
     [-max_num_level max_num_level] 
     [-coarsening_ratio coarsening_ratio]
     [-large_net_threshold large_net_threshold]
-    [-signature_net_threshold signature_net_threshold]
     [-halo_width halo_width] 
     [-halo_height halo_height]
     [-fence_lx fence_lx] 
@@ -59,7 +58,6 @@ rtl_macro_placer
 | `-max_num_level` | Maximum depth of physical hierarchical tree. The default value is `2`, and the allowed values are integers `[0, MAX_INT]`. |
 | `-coarsening_ratio` | The larger the coarsening_ratio, the faster the convergence process. The allowed values are floats, and the default value is `10.0`. |
 | `-large_net_threshold` | Ignore nets with many connections during clustering, such as global nets. The default value is `50`, and the allowed values are integers `[0, MAX_INT]`. |
-| `-signature_net_threshold` | Minimum number of connections between two clusters to be identified as connected. The default value is `50`, and the allowed values are integers `[0, MAX_INT]`. |
 | `-halo_width` | Horizontal/vertical halo around macros (microns). The allowed values are floats, and the default value is `0.0`. |
 | `-fence_lx`, `-fence_ly`, `-fence_ux`, `-fence_uy` | Defines the global fence bounding box coordinates. The default values are the core area coordinates). |
 | `-target_util` | Specifies the target utilization of `MixedCluster` and has higher priority than target_dead_space. The allowed values are floats, and the default value is `0.25`. |

src/mpl/include/mpl/rtl_mp.h

@@ -51,7 +51,6 @@ class MacroPlacer
              int max_num_level,
              float coarsening_ratio,
              int large_net_threshold,
-             int signature_net_threshold,
              float halo_width,
              float halo_height,
              float fence_lx,

src/mpl/src/clusterEngine.cpp

@@ -1743,23 +1743,10 @@ void ClusteringEngine::mergeChildrenBelowThresholds(
     }
     // Firstly we perform Type 1 merge
     for (int i = 0; i < num_small_children; i++) {
-      const int cluster_id = small_children[i]->getCloseCluster(
-          small_children_ids, tree_->min_net_count_for_connection);
-      debugPrint(
-          logger_,
-          MPL,
-          "multilevel_autoclustering",
-          1,
-          "Candidate cluster: {} - {}",
-          small_children[i]->getName(),
-          (cluster_id != -1 ? tree_->maps.id_to_cluster[cluster_id]->getName()
-                            : "   "));
-      if (cluster_id != -1
-          && !tree_->maps.id_to_cluster[cluster_id]->isIOCluster()) {
-        Cluster* close_cluster = tree_->maps.id_to_cluster[cluster_id];
-        if (attemptMerge(close_cluster, small_children[i])) {
-          cluster_class[i] = close_cluster->getId();
-        }
+      Cluster* close_cluster = findSingleWellFormedConnectedCluster(
+          small_children[i], small_children_ids);
+      if (close_cluster && attemptMerge(close_cluster, small_children[i])) {
+        cluster_class[i] = close_cluster->getId();
       }
     }
 
@@ -1772,8 +1759,7 @@ void ClusteringEngine::mergeChildrenBelowThresholds(
             continue;
           }
 
-          if (small_children[i]->isSameConnSignature(
-                  *small_children[j], tree_->min_net_count_for_connection)) {
+          if (sameConnectionSignature(small_children[i], small_children[j])) {
             if (attemptMerge(small_children[i], small_children[j])) {
               cluster_class[j] = i;
             } else {
@@ -1860,6 +1846,129 @@ void ClusteringEngine::mergeChildrenBelowThresholds(
              "Finished merging clusters");
 }
 
+bool ClusteringEngine::sameConnectionSignature(Cluster* a, Cluster* b) const
+{
+  std::vector<int> a_neighbors = findNeighbors(a, /* ignore */ b);
+  if (a_neighbors.empty()) {
+    return false;
+  }
+
+  std::vector<int> b_neighbors = findNeighbors(b, /* ignore */ a);
+  if (b_neighbors.size() != a_neighbors.size()) {
+    return false;
+  }
+
+  std::sort(a_neighbors.begin(), a_neighbors.end());
+  std::sort(b_neighbors.begin(), b_neighbors.end());
+
+  for (int i = 0; i < a_neighbors.size(); i++) {
+    if (a_neighbors[i] != b_neighbors[i]) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+std::vector<int> ClusteringEngine::findNeighbors(Cluster* target_cluster,
+                                                 Cluster* ignored_cluster) const
+{
+  std::vector<int> neighbors;
+  const ConnectionsMap& target_connections
+      = target_cluster->getConnectionsMap();
+
+  for (const auto& [cluster_id, connection_weight] : target_connections) {
+    if (cluster_id == target_cluster->getId()) {
+      logger_->error(MPL,
+                     53,
+                     "Cluster {} is connected to itself.",
+                     target_cluster->getName());
+    }
+
+    if (cluster_id == ignored_cluster->getId()) {
+      continue;
+    }
+
+    const float connection_ratio
+        = connection_weight / target_cluster->allConnectionsWeight();
+
+    if (connection_ratio >= minimum_connection_ratio_) {
+      neighbors.push_back(cluster_id);
+    }
+  }
+
+  return neighbors;
+}
+
+bool ClusteringEngine::strongConnection(Cluster* a,
+                                        Cluster* b,
+                                        const float* connection_weight) const
+{
+  if (a == b) {
+    logger_->error(
+        MPL,
+        61,
+        "Attempt to evaluate if cluster {} has strong connection with itself.",
+        a->getName());
+  }
+
+  // Attention that we need to subtract the weight of the connection that
+  // we're evaluating otherwise we'll be taking it into account twice.
+  float total_weight = a->allConnectionsWeight() + b->allConnectionsWeight();
+  float connection_ratio = 0.0;
+  if (connection_weight) {
+    total_weight -= *connection_weight;
+    connection_ratio = *connection_weight / total_weight;
+  } else {
+    const ConnectionsMap& a_connections = a->getConnectionsMap();
+    auto itr = a_connections.find(b->getId());
+
+    if (itr != a_connections.end()) {
+      const float conn_weight = itr->second;
+      total_weight -= conn_weight;
+      connection_ratio = conn_weight / total_weight;
+    }
+  }
+
+  return connection_ratio >= minimum_connection_ratio_;
+}
+
+Cluster* ClusteringEngine::findSingleWellFormedConnectedCluster(
+    Cluster* target_cluster,
+    const std::vector<int>& small_clusters_id_list) const
+{
+  int number_of_close_clusters = 0;
+  Cluster* close_cluster = nullptr;
+  const ConnectionsMap& target_connections
+      = target_cluster->getConnectionsMap();
+
+  for (auto& [cluster_id, connection_weight] : target_connections) {
+    Cluster* candidate = tree_->maps.id_to_cluster.at(cluster_id);
+
+    if (candidate->isIOCluster()) {
+      continue;
+    }
+
+    if (strongConnection(target_cluster, candidate, &connection_weight)) {
+      auto small_child_found = std::find(small_clusters_id_list.begin(),
+                                         small_clusters_id_list.end(),
+                                         cluster_id);
+
+      // A small child is not well-formed, so we avoid them.
+      if (small_child_found == small_clusters_id_list.end()) {
+        number_of_close_clusters++;
+        close_cluster = candidate;
+      }
+    }
+  }
+
+  if (number_of_close_clusters == 1) {
+    return close_cluster;
+  }
+
+  return nullptr;
+}
+
 bool ClusteringEngine::attemptMerge(Cluster* receiver, Cluster* incomer)
 {
   // Cache incomer data in case it is deleted.
@@ -1910,6 +2019,8 @@ void ClusteringEngine::clearConnections()
 
 void ClusteringEngine::buildNetListConnections()
 {
+  const float connection_weight = 1.0;
+
   for (odb::dbNet* net : block_->getNets()) {
     if (!isValidNet(net)) {
       continue;
@@ -1929,11 +2040,9 @@ void ClusteringEngine::buildNetListConnections()
       }
     }
 
-    bool net_has_io_pin = false;
     if (tree_->io_pads.empty()) {
       for (odb::dbBTerm* bterm : net->getBTerms()) {
         const int cluster_id = tree_->maps.bterm_to_cluster_id.at(bterm);
-        net_has_io_pin = true;
 
         if (bterm->getIoType() == odb::dbIoType::INPUT) {
           driver_cluster_id = cluster_id;
@@ -1945,13 +2054,12 @@ void ClusteringEngine::buildNetListConnections()
 
     if (driver_cluster_id != -1 && !load_clusters_ids.empty()
         && load_clusters_ids.size() < tree_->large_net_threshold) {
-      const float weight = net_has_io_pin ? tree_->virtual_weight : 1.0;
       Cluster* driver_cluster = tree_->maps.id_to_cluster.at(driver_cluster_id);
 
       for (const int load_cluster_id : load_clusters_ids) {
         if (load_cluster_id != driver_cluster_id) {
           Cluster* load_cluster = tree_->maps.id_to_cluster.at(load_cluster_id);
-          connect(driver_cluster, load_cluster, weight);
+          connect(driver_cluster, load_cluster, connection_weight);
         }
       }
     }
@@ -2210,8 +2318,7 @@ void ClusteringEngine::classifyMacrosByConnSignature(
           continue;
         }
 
-        if (macro_clusters[i]->isSameConnSignature(
-                *macro_clusters[j], tree_->min_net_count_for_connection)) {
+        if (sameConnectionSignature(macro_clusters[i], macro_clusters[j])) {
           signature_class[j] = i;
         }
       }
@@ -2239,8 +2346,11 @@ void ClusteringEngine::classifyMacrosByInterconn(
     if (interconn_class[i] == -1) {
       interconn_class[i] = i;
       for (int j = 0; j < macro_clusters.size(); j++) {
-        if (macro_clusters[i]->hasMacroConnectionWith(
-                *macro_clusters[j], tree_->min_net_count_for_connection)) {
+        if (macro_clusters[i] == macro_clusters[j]) {
+          continue;
+        }
+
+        if (strongConnection(macro_clusters[i], macro_clusters[j])) {
           if (interconn_class[j] != -1) {
             interconn_class[i] = interconn_class[j];
             break;

src/mpl/src/clusterEngine.h

@@ -117,7 +117,6 @@ struct PhysicalHierarchy
 
   int max_level{0};
   int large_net_threshold{0};  // used to ignore global nets
-  int min_net_count_for_connection{0};
   float cluster_size_ratio{0.0f};
   float cluster_size_tolerance{0.0f};
 
@@ -212,6 +211,15 @@ class ClusteringEngine
   bool partitionerSolutionIsFullyUnbalanced(const std::vector<int>& solution,
                                             int num_other_cluster_vertices);
   void mergeChildrenBelowThresholds(std::vector<Cluster*>& small_children);
+  bool sameConnectionSignature(Cluster* a, Cluster* b) const;
+  bool strongConnection(Cluster* a,
+                        Cluster* b,
+                        const float* connection_weight = nullptr) const;
+  Cluster* findSingleWellFormedConnectedCluster(
+      Cluster* target_cluster,
+      const std::vector<int>& small_clusters_id_list) const;
+  std::vector<int> findNeighbors(Cluster* target_cluster,
+                                 Cluster* ignored_cluster) const;
   bool attemptMerge(Cluster* receiver, Cluster* incomer);
   void fetchMixedLeaves(Cluster* parent,
                         std::vector<std::vector<Cluster*>>& mixed_leaves);
@@ -304,6 +312,8 @@ class ClusteringEngine
   // them to be considered connected when creating data flow.
   const int max_num_of_hops_ = 5;
 
+  const float minimum_connection_ratio_{0.08};
+
   int first_io_bundle_id_{-1};
   IOBundleSpans io_bundle_spans_;
 };

src/mpl/src/hier_rtlmp.cpp

@@ -158,11 +158,6 @@ void HierRTLMP::setLargeNetThreshold(int large_net_threshold)
   tree_->large_net_threshold = large_net_threshold;
 }
 
-void HierRTLMP::setSignatureNetThreshold(int signature_net_threshold)
-{
-  tree_->min_net_count_for_connection = signature_net_threshold;
-}
-
 void HierRTLMP::setTargetUtil(float target_util)
 {
   target_util_ = target_util;
@@ -2170,7 +2165,7 @@ void HierRTLMP::placeMacros(Cluster* cluster)
 
     // Large arrays need more steps to properly converge.
     if (large_macro_cluster) {
-      perturbations_per_step *= 2;
+      perturbations_per_step = num_perturb_per_step_;
     }
   }
 

src/mpl/src/hier_rtlmp.h

@@ -92,7 +92,6 @@ class HierRTLMP
   void setMaxNumLevel(int max_num_level);
   void setClusterSizeRatioPerLevel(float coarsening_ratio);
   void setLargeNetThreshold(int large_net_threshold);
-  void setSignatureNetThreshold(int signature_net_threshold);
   void setAreaWeight(float area_weight);
   void setOutlineWeight(float outline_weight);
   void setWirelengthWeight(float wirelength_weight);

src/mpl/src/mpl.i

@@ -34,7 +34,6 @@ bool rtl_macro_placer_cmd(const int max_num_macro,
                           const int max_num_level,
                           const float coarsening_ratio,
                           const int large_net_threshold,
-                          const int signature_net_threshold,
                           const float halo_width,
                           const float halo_height,
                           const float fence_lx,
@@ -66,7 +65,6 @@ bool rtl_macro_placer_cmd(const int max_num_macro,
                              max_num_level,
                              coarsening_ratio,
                              large_net_threshold,
-                             signature_net_threshold,
                              halo_width,
                              halo_height,
                              fence_lx,

src/mpl/src/mpl.tcl

@@ -9,7 +9,6 @@ sta::define_cmd_args "rtl_macro_placer" { -max_num_macro  max_num_macro \
                                           -max_num_level  max_num_level \
                                           -coarsening_ratio coarsening_ratio \
                                           -large_net_threshold large_net_threshold \
-                                          -signature_net_threshold signature_net_threshold \
                                           -halo_width halo_width \
                                           -halo_height halo_height \
                                           -fence_lx   fence_lx \
@@ -35,7 +34,7 @@ proc rtl_macro_placer { args } {
   sta::parse_key_args "rtl_macro_placer" args \
     keys {-max_num_macro  -min_num_macro -max_num_inst  -min_num_inst  -tolerance   \
          -max_num_level  -coarsening_ratio -large_net_threshold \
-         -signature_net_threshold -halo_width -halo_height \
+         -halo_width -halo_height \
          -fence_lx   -fence_ly  -fence_ux   -fence_uy  \
          -area_weight  -outline_weight -wirelength_weight -guidance_weight -fence_weight \
          -boundary_weight -notch_weight \
@@ -63,7 +62,6 @@ proc rtl_macro_placer { args } {
   set max_num_level 2
   set coarsening_ratio 10.0
   set large_net_threshold 50
-  set signature_net_threshold 50
   set halo_width 0.0
   set halo_height 0.0
   set fence_lx 0.0
@@ -110,9 +108,6 @@ proc rtl_macro_placer { args } {
   if { [info exists keys(-large_net_threshold)] } {
     set large_net_threshold $keys(-large_net_threshold)
   }
-  if { [info exists keys(-signature_net_threshold)] } {
-    set signature_net_threshold $keys(-signature_net_threshold)
-  }
 
   if { [info exists keys(-halo_width)] && [info exists keys(-halo_height)] } {
     set halo_width $keys(-halo_width)
@@ -189,7 +184,6 @@ proc rtl_macro_placer { args } {
       $max_num_level \
       $coarsening_ratio \
       $large_net_threshold \
-      $signature_net_threshold \
       $halo_width \
       $halo_height \
       $fence_lx $fence_ly $fence_ux $fence_uy \