Bug 1828862 - Improve caching of knowledge of listeners which the event listener manager does not have, r=masayuki

Differential Revision: https://phabricator.services.mozilla.com/D175855

dom/events/EventListenerManager.cpp

@@ -100,8 +100,7 @@ static uint32_t MutationBitForEventType(EventMessage aEventType) {
 uint32_t EventListenerManager::sMainThreadCreatedCount = 0;
 
 EventListenerManagerBase::EventListenerManagerBase()
-    : mNoListenerForEvent(eVoidEvent),
-      mMayHavePaintEventListener(false),
+    : mMayHavePaintEventListener(false),
       mMayHaveMutationListeners(false),
       mMayHaveCapturingListeners(false),
       mMayHaveSystemGroupListeners(false),
@@ -117,7 +116,8 @@ EventListenerManagerBase::EventListenerManagerBase()
       mIsMainThreadELM(NS_IsMainThread()),
       mHasNonPrivilegedClickListeners(false),
       mUnknownNonPrivilegedClickListeners(false) {
-  static_assert(sizeof(EventListenerManagerBase) == sizeof(uint32_t),
+  ClearNoListenersForEvents();
+  static_assert(sizeof(EventListenerManagerBase) == sizeof(uint64_t),
                 "Keep the size of EventListenerManagerBase size compact!");
 }
 
@@ -238,7 +238,7 @@ void EventListenerManager::AddEventListenerInternal(
     }
   }
 
-  mNoListenerForEvent = eVoidEvent;
+  ClearNoListenersForEvents();
   mNoListenerForEventAtom = nullptr;
 
   listener =
@@ -789,7 +789,7 @@ void EventListenerManager::DisableDevice(EventMessage aEventMessage) {
 void EventListenerManager::NotifyEventListenerRemoved(nsAtom* aUserType) {
   // If the following code is changed, other callsites of EventListenerRemoved
   // and NotifyAboutMainThreadListenerChange should be changed too.
-  mNoListenerForEvent = eVoidEvent;
+  ClearNoListenersForEvents();
   mNoListenerForEventAtom = nullptr;
   if (mTarget) {
     mTarget->EventListenerRemoved(aUserType);
@@ -1566,8 +1566,13 @@ void EventListenerManager::HandleEventInternal(nsPresContext* aPresContext,
   }
 
   if (mIsMainThreadELM && !hasListener) {
-    mNoListenerForEvent = aEvent->mMessage;
-    mNoListenerForEventAtom = aEvent->mSpecifiedEventType;
+    if (aEvent->mMessage != eUnidentifiedEvent) {
+      mNoListenerForEvents[2] = mNoListenerForEvents[1];
+      mNoListenerForEvents[1] = mNoListenerForEvents[0];
+      mNoListenerForEvents[0] = aEvent->mMessage;
+    } else {
+      mNoListenerForEventAtom = aEvent->mSpecifiedEventType;
+    }
   }
 
   if (aEvent->DefaultPrevented()) {
@@ -1849,7 +1854,7 @@ nsresult EventListenerManager::SetListenerEnabled(
   if (aEnabled) {
     // We may have enabled some listener, clear the cache for which events
     // we don't have listeners.
-    mNoListenerForEvent = eVoidEvent;
+    ClearNoListenersForEvents();
     mNoListenerForEventAtom = nullptr;
   }
   return NS_OK;

dom/events/EventListenerManager.h

@@ -145,7 +145,13 @@ class EventListenerManagerBase {
  protected:
   EventListenerManagerBase();
 
-  EventMessage mNoListenerForEvent;
+  void ClearNoListenersForEvents() {
+    mNoListenerForEvents[0] = eVoidEvent;
+    mNoListenerForEvents[1] = eVoidEvent;
+    mNoListenerForEvents[2] = eVoidEvent;
+  }
+
+  EventMessage mNoListenerForEvents[3];
   uint16_t mMayHavePaintEventListener : 1;
   uint16_t mMayHaveMutationListeners : 1;
   uint16_t mMayHaveCapturingListeners : 1;
@@ -387,9 +393,13 @@ class EventListenerManager final : public EventListenerManagerBase {
     }
 
     // Check if we already know that there is no event listener for the event.
-    if (mNoListenerForEvent == aEvent->mMessage &&
-        (mNoListenerForEvent != eUnidentifiedEvent ||
-         mNoListenerForEventAtom == aEvent->mSpecifiedEventType)) {
+    if (aEvent->mMessage == eUnidentifiedEvent) {
+      if (mNoListenerForEventAtom == aEvent->mSpecifiedEventType) {
+        return;
+      }
+    } else if (mNoListenerForEvents[0] == aEvent->mMessage ||
+               mNoListenerForEvents[1] == aEvent->mMessage ||
+               mNoListenerForEvents[2] == aEvent->mMessage) {
       return;
     }
     HandleEventInternal(aPresContext, aEvent, aDOMEvent, aCurrentTarget,