mpl2: throw error when PAR gives MPL2 a completely unbalanced solution

Signed-off-by: Arthur Koucher <arthurkoucher@precisioninno.com>

src/mpl2/src/clusterEngine.cpp

@@ -1452,6 +1452,14 @@ void ClusteringEngine::breakLargeFlatCluster(Cluster* parent)
                                               vertex_weight,
                                               hyperedge_weights);
 
+  if (partitionerSolutionIsFullyUnbalanced(part, num_other_cluster_vertices)) {
+    logger_->error(MPL,
+                   37,
+                   "Couldn't break flat cluster {} with PAR. The solution is "
+                   "fully unbalanced.",
+                   parent->getName());
+  }
+
   parent->clearLeafStdCells();
   parent->clearLeafMacros();
 
@@ -1481,6 +1489,27 @@ void ClusteringEngine::breakLargeFlatCluster(Cluster* parent)
   breakLargeFlatCluster(raw_part_1);
 }
 
+bool ClusteringEngine::partitionerSolutionIsFullyUnbalanced(
+    const std::vector<int>& solution,
+    const int num_other_cluster_vertices)
+{
+  // The partition of the first vertex which represents
+  // an actual macro or std cell.
+  const int first_vertex_partition = solution[num_other_cluster_vertices];
+  const int number_of_vertices = static_cast<int>(solution.size());
+
+  // Skip all the vertices that represents other clusters.
+  for (int vertex_id = num_other_cluster_vertices;
+       vertex_id < number_of_vertices;
+       ++vertex_id) {
+    if (solution[vertex_id] != first_vertex_partition) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
 // Recursively merge children whose number of std cells and macro
 // is below the current level thresholds. There are three cases:
 // 1) Children are closely connected.

src/mpl2/src/clusterEngine.h

@@ -194,6 +194,8 @@ class ClusteringEngine
   void createCluster(Cluster* parent);
   void updateSubTree(Cluster* parent);
   void breakLargeFlatCluster(Cluster* parent);
+  bool partitionerSolutionIsFullyUnbalanced(const std::vector<int>& solution,
+                                            int num_other_cluster_vertices);
   void mergeChildrenBelowThresholds(std::vector<Cluster*>& small_children);
   bool attemptMerge(Cluster* receiver, Cluster* incomer);
   void fetchMixedLeaves(Cluster* parent,