diff --git a/liberty/Liberty.cc b/liberty/Liberty.cc
index 57f9f388..0eef87c4 100644
--- a/liberty/Liberty.cc
+++ b/liberty/Liberty.cc
@@ -1029,17 +1029,21 @@ LibertyCell::setClockGateType(ClockGateType type)
 bool
 LibertyCell::isBuffer() const
 {
-  if (ports_.size() == 2) {
-    LibertyPort *port1 = static_cast<LibertyPort*>(ports_[0]);
-    LibertyPort *port2 = static_cast<LibertyPort*>(ports_[1]);
-    return (port1->direction()->isInput()
-	    && port2->direction()->isOutput()
-	    && hasBufferFunc(port1, port2))
-      || (port2->direction()->isInput()
-	  && port1->direction()->isOutput()
-	  && hasBufferFunc(port2, port1));
+  int input_count = 0;
+  int output_count = 0;
+  for (ConcretePort *cport : ports_) {
+    LibertyPort *port = static_cast<LibertyPort*>(cport);
+    PortDirection *dir = port->direction();
+    if (dir->isInput())
+      input_count++;
+    else if (dir->isOutput())
+      output_count++;
+    else if (!dir->isPowerGround())
+      return false;
+    if (input_count > 1 || output_count > 1)
+      break;
   }
-  return false;
+  return input_count == 1 && output_count == 1;
 }
 
 bool
@@ -1057,17 +1061,18 @@ LibertyCell::bufferPorts(// Return values.
 			 LibertyPort *&input,
 			 LibertyPort *&output)
 {
-    LibertyPort *port1 = static_cast<LibertyPort*>(ports_[0]);
-    LibertyPort *port2 = static_cast<LibertyPort*>(ports_[1]);
-    if (port1->direction()->isInput()
-	&& port2->direction()->isOutput()) {
-      input = port1;
-      output = port2;
-    }
-    else {
-      input = port2;
-      output = port1;
-    }
+  input = nullptr;
+  output = nullptr;
+  for (ConcretePort *cport : ports_) {
+    LibertyPort *port = static_cast<LibertyPort*>(cport);
+    PortDirection *dir = port->direction();
+    if (dir->isInput())
+      input = port;
+    else if (dir->isOutput())
+      output = port;
+    if (input && output)
+      return;
+  }
 }
 
 unsigned
diff --git a/network/Network.cc b/network/Network.cc
index f577034f..1c172159 100644
--- a/network/Network.cc
+++ b/network/Network.cc
@@ -1077,7 +1077,7 @@ LeafInstanceIterator1::LeafInstanceIterator1(const Instance *inst,
   child_iter_(network->childIterator(inst)),
   next_(nullptr)
 {
-  pending_child_iters_.reserve(512);
+  pending_child_iters_.reserve(8);
   nextInst();
 }
 
diff --git a/search/Sim.cc b/search/Sim.cc
index 624a3f44..53d787a7 100644
--- a/search/Sim.cc
+++ b/search/Sim.cc
@@ -579,9 +579,9 @@ Sim::propagateToInvalidLoads()
   while (load_iter.hasNext()) {
     Pin *load_pin = load_iter.next();
     Net *net = network_->net(load_pin);
-    if (network_->isGround(net))
+    if (net && network_->isGround(net))
       setPinValue(load_pin, LogicValue::zero, true);
-    else if (network_->isPower(net))
+    else if (net && network_->isPower(net))
       setPinValue(load_pin, LogicValue::one, true);
     else {
       Pin *drvr_pin = findDrvrPin(load_pin, network_);
@@ -701,9 +701,14 @@ Sim::connectPinAfter(Pin *pin)
 void
 Sim::disconnectPinBefore(Pin *pin)
 {
-  if (incremental_
-      && network_->isLoad(pin))
-    removePropagatedValue(pin);
+  if (incremental_) {
+    if (network_->isLoad(pin)) {
+      invalid_load_pins_.insert(pin);
+      removePropagatedValue(pin);
+    }
+    if (network_->isDriver(pin))
+      invalid_drvr_pins_.insert(pin);
+  }
 }
 
 void