Merge pull request #9259 from luis201420/cts_fix_defined_fanout

CTS: fix the correct value of max fanout

Author: maliberty

src/cts/src/TritonCTS.cpp

@@ -143,6 +143,15 @@ int TritonCTS::getBufferFanoutLimit(const std::string& bufferName)
   int fanout = std::numeric_limits<int>::max();
   float tempFanout;
   bool existMaxFanout;
+
+  // Check if top instance has fanout limit
+  sta::Cell* top_cell = network_->cell(network_->topInstance());
+  openSta_->sdc()->fanoutLimit(
+      top_cell, sta::MinMax::max(), tempFanout, existMaxFanout);
+  if (existMaxFanout) {
+    fanout = std::min(fanout, (int) tempFanout);
+  }
+
   odb::dbMaster* bufferMaster = db_->findMaster(bufferName.c_str());
   sta::Cell* bufferCell = network_->dbToSta(bufferMaster);
   sta::Port* buffer_port = nullptr;
@@ -159,7 +168,7 @@ int TritonCTS::getBufferFanoutLimit(const std::string& bufferName)
     }
   }
   if (buffer_port == nullptr) {
-    return 0;
+    return (existMaxFanout) ? fanout : 0;
   }
 
   openSta_->sdc()->fanoutLimit(