diff --git a/power/Power.cc b/power/Power.cc
index cc596820..48692dea 100644
--- a/power/Power.cc
+++ b/power/Power.cc
@@ -101,6 +101,7 @@ Power::Power(StaState *sta) :
   seq_activity_map_(100, SeqPinHash(network_), SeqPinEqual()),
   activities_valid_(false),
   bdd_(sta),
+  instance_powers_valid_(false),
   corner_(nullptr)
 {
 }
@@ -118,19 +119,26 @@ Power::clear()
   corner_ = nullptr;
 }
 
+void
+Power::activitiesInvalid()
+{
+  activities_valid_ = false;
+  instance_powers_valid_ = false;
+}
+
 void
 Power::setGlobalActivity(float density,
 			 float duty)
 {
   global_activity_.set(density, duty, PwrActivityOrigin::global);
-  activities_valid_ = false;
+  activitiesInvalid();
 }
   
 void
 Power::unsetGlobalActivity()
 {
   global_activity_.init();
-  activities_valid_ = false;
+  activitiesInvalid();
 }
 
 void
@@ -138,14 +146,14 @@ Power::setInputActivity(float density,
 			float duty)
 {
   input_activity_.set(density, duty, PwrActivityOrigin::input);
-  activities_valid_ = false;
+  activitiesInvalid();
 }
 
 void
 Power::unsetInputActivity()
 {
   input_activity_.init();
-  activities_valid_ = false;
+  activitiesInvalid();
 }
 
 void
@@ -157,7 +165,7 @@ Power::setInputPortActivity(const Port *input_port,
   const Pin *pin = network_->findPin(top_inst, input_port);
   if (pin) {
     user_activity_map_[pin] = {density, duty, PwrActivityOrigin::user};
-    activities_valid_ = false;
+    activitiesInvalid();
   }
 }
 
@@ -168,7 +176,7 @@ Power::unsetInputPortActivity(const Port *input_port)
   const Pin *pin = network_->findPin(top_inst, input_port);
   if (pin) {
     user_activity_map_.erase(pin);
-    activities_valid_ = false;
+    activitiesInvalid();
   }
 }
 
@@ -179,14 +187,14 @@ Power::setUserActivity(const Pin *pin,
                        PwrActivityOrigin origin)
 {
   user_activity_map_[pin] = {density, duty, origin};
-  activities_valid_ = false;
+  activitiesInvalid();
 }
 
 void
 Power::unsetUserActivity(const Pin *pin)
 {
   user_activity_map_.erase(pin);
-  activities_valid_ = false;
+  activitiesInvalid();
 }
 
 PwrActivity &
@@ -233,7 +241,7 @@ Power::setSeqActivity(const Instance *reg,
 		      PwrActivity &activity)
 {
   seq_activity_map_[SeqPin(reg, output)] = activity;
-  activities_valid_ = false;
+  activitiesInvalid();
 }
 
 bool
@@ -699,10 +707,9 @@ void
 Power::ensureActivities()
 {
   Stats stats(debug_, report_);
-  // No need to propagate activites if global activity is set.
-  if (!global_activity_.isSet()) {
-    if (!activities_valid_) {
-      Stats stats(debug_, report_);
+  if (!activities_valid_) {
+    // No need to propagate activites if global activity is set.
+    if (!global_activity_.isSet()) {
       // Clear existing activities.
       activity_map_.clear();
       seq_activity_map_.clear();
@@ -738,9 +745,8 @@ Power::ensureActivities()
                    pass, visitor.maxChange());
         pass++;
       }
-      stats.report("Find power activities");
-      activities_valid_ = true;
     }
+    activities_valid_ = true;
   }
   stats.report("Power activities");
 }
@@ -837,9 +843,11 @@ Power::seedRegOutputActivities(const Instance *reg,
 void
 Power::ensureInstPowers(const Corner *corner)
 {
-  if (instance_powers_.empty()
-      || corner != corner_)
+  if (!instance_powers_valid_
+      || corner != corner_) {
     findInstPowers(corner);
+    instance_powers_valid_ = true;
+  }
 }
 
 void
diff --git a/power/Power.hh b/power/Power.hh
index e51ce285..55f8a252 100644
--- a/power/Power.hh
+++ b/power/Power.hh
@@ -76,6 +76,7 @@ class Power : public StaState
 public:
   Power(StaState *sta);
   void clear();
+  void activitiesInvalid();
   void power(const Corner *corner,
 	     // Return values.
 	     PowerResult &total,
@@ -234,6 +235,7 @@ private:
   bool activities_valid_;
   Bdd bdd_;
   std::map<const Instance*, PowerResult> instance_powers_;
+  bool instance_powers_valid_;
   const Corner *corner_;
 
   static constexpr int max_activity_passes_ = 100;
diff --git a/search/Sta.cc b/search/Sta.cc
index b34d2d8a..3957f3d5 100644
--- a/search/Sta.cc
+++ b/search/Sta.cc
@@ -1111,6 +1111,7 @@ Sta::makeClock(const char *name,
   sdc_->makeClock(name, pins, add_to_pins, period, waveform, comment);
   update_genclks_ = true;
   search_->arrivalsInvalid();
+  power_->activitiesInvalid();
 }
 
 void
@@ -1135,6 +1136,7 @@ Sta::makeGeneratedClock(const char *name,
 			   edges, edge_shifts, comment);
   update_genclks_ = true;
   search_->arrivalsInvalid();
+  power_->activitiesInvalid();
 }
 
 void
@@ -1142,6 +1144,7 @@ Sta::removeClock(Clock *clk)
 {
   sdc_->removeClock(clk);
   search_->arrivalsInvalid();
+  power_->activitiesInvalid();
 }
 
 bool
@@ -1819,6 +1822,7 @@ Sta::setLogicValue(Pin *pin,
   sdc_->setLogicValue(pin, value);
   // Levelization respects constant disabled edges.
   levelize_->invalid();
+  power_->activitiesInvalid();
   sim_->constantsInvalid();
   // Constants disable edges which isolate downstream vertices of the
   // graph from the delay calculator's BFS search.  This means that
@@ -1834,6 +1838,7 @@ Sta::setCaseAnalysis(Pin *pin,
 		     LogicValue value)
 {
   sdc_->setCaseAnalysis(pin, value);
+  power_->activitiesInvalid();
   // Levelization respects constant disabled edges.
   levelize_->invalid();
   sim_->constantsInvalid();
diff --git a/verilog/VerilogReader.cc b/verilog/VerilogReader.cc
index f9ea77e9..166021e6 100644
--- a/verilog/VerilogReader.cc
+++ b/verilog/VerilogReader.cc
@@ -534,7 +534,7 @@ VerilogReader::makeModuleInst(const string *module_vname,
   // to reduce the memory footprint of the verilog parser.
   if (liberty_cell
       && hasScalarNamedPortRefs(liberty_cell, pins)) {
-    int port_count = liberty_cell->portBitCount();
+    const int port_count = liberty_cell->portBitCount();
     StdStringSeq net_names(port_count);
     for (VerilogNet *vnet : *pins) {
       VerilogNetPortRefScalarNet *vpin =