Bug 1385459 - Don't use QI to canonicalize nsISupports pointers in the purple buffer. r=smaug

The nsISupports objects added to the purple buffer are already
canonical, so we can avoid some overhead by not QIing them to
nsCycleCollectionISupports. This QIing overhead shows up in profiles.

MozReview-Commit-ID: CQN6wwc7MZm

--HG--
extra : rebase_source : 27e6b70f83b42b5db7af3d1e7d62e36d6f4013a0

xpcom/base/nsCycleCollector.cpp

@@ -956,27 +956,6 @@ CanonicalizeXPCOMParticipant(nsISupports* aIn)
   return out;
 }
 
-static inline void
-ToParticipant(nsISupports* aPtr, nsXPCOMCycleCollectionParticipant** aCp);
-
-static void
-CanonicalizeParticipant(void** aParti, nsCycleCollectionParticipant** aCp)
-{
-  // If the participant is null, this is an nsISupports participant,
-  // so we must QI to get the real participant.
-
-  if (!*aCp) {
-    nsISupports* nsparti = static_cast<nsISupports*>(*aParti);
-    nsparti = CanonicalizeXPCOMParticipant(nsparti);
-    NS_ASSERTION(nsparti,
-                 "Don't add objects that don't participate in collection!");
-    nsXPCOMCycleCollectionParticipant* xcp;
-    ToParticipant(nsparti, &xcp);
-    *aParti = nsparti;
-    *aCp = xcp;
-  }
-}
-
 struct nsPurpleBufferEntry
 {
   nsPurpleBufferEntry(void* aObject, nsCycleCollectingAutoRefCnt* aRefCnt,
@@ -1426,6 +1405,21 @@ ToParticipant(nsISupports* aPtr, nsXPCOMCycleCollectionParticipant** aCp)
   CallQueryInterface(aPtr, aCp);
 }
 
+static void
+ToParticipant(void* aParti, nsCycleCollectionParticipant** aCp)
+{
+  // If the participant is null, this is an nsISupports participant,
+  // so we must QI to get the real participant.
+
+  if (!*aCp) {
+    nsISupports* nsparti = static_cast<nsISupports*>(aParti);
+    MOZ_ASSERT(CanonicalizeXPCOMParticipant(nsparti) == nsparti);
+    nsXPCOMCycleCollectionParticipant* xcp;
+    ToParticipant(nsparti, &xcp);
+    *aCp = xcp;
+  }
+}
+
 template<class Visitor>
 MOZ_NEVER_INLINE void
 GraphWalker<Visitor>::Walk(PtrInfo* aPi)
@@ -2234,7 +2228,7 @@ CCGraphBuilder::AddNode(void* aPtr, nsCycleCollectionParticipant* aParticipant)
 bool
 CCGraphBuilder::AddPurpleRoot(void* aRoot, nsCycleCollectionParticipant* aParti)
 {
-  CanonicalizeParticipant(&aRoot, &aParti);
+  ToParticipant(aRoot, &aParti);
 
   if (WantAllTraces() || !aParti->CanSkipInCC(aRoot)) {
     PtrInfo* pinfo = AddNode(aRoot, aParti);
@@ -2670,7 +2664,7 @@ public:
     if (!aEntry->mRefCnt->get()) {
       void* o = aEntry->mObject;
       nsCycleCollectionParticipant* cp = aEntry->mParticipant;
-      CanonicalizeParticipant(&o, &cp);
+      ToParticipant(o, &cp);
       SnowWhiteObject swo = { o, cp, aEntry->mRefCnt };
       mObjects.InfallibleAppend(swo);
       aBuffer.Remove(aEntry);
@@ -2796,7 +2790,7 @@ public:
     }
     void* o = aEntry->mObject;
     nsCycleCollectionParticipant* cp = aEntry->mParticipant;
-    CanonicalizeParticipant(&o, &cp);
+    ToParticipant(o, &cp);
     if (aEntry->mRefCnt->IsPurple() && !cp->CanSkip(o, false) &&
         (!mRemoveChildlessNodes || MayHaveChild(o, cp))) {
       return true;
@@ -3003,10 +2997,9 @@ public:
                "Snow-white objects shouldn't be in the purple buffer.");
 
     void* obj = aEntry->mObject;
-    if (!aEntry->mParticipant) {
-      obj = CanonicalizeXPCOMParticipant(static_cast<nsISupports*>(obj));
-      MOZ_ASSERT(obj, "Don't add objects that don't participate in collection!");
-    }
+
+    MOZ_ASSERT(aEntry->mParticipant || CanonicalizeXPCOMParticipant(static_cast<nsISupports*>(obj)) == obj,
+               "Suspect nsISupports pointer must be canonical");
 
     PtrInfo* pi = mGraph.FindNode(obj);
     if (!pi) {
@@ -3489,6 +3482,9 @@ nsCycleCollector::Suspect(void* aPtr, nsCycleCollectionParticipant* aParti,
   MOZ_ASSERT(HasParticipant(aPtr, aParti),
              "Suspected nsISupports pointer must QI to nsXPCOMCycleCollectionParticipant");
 
+  MOZ_ASSERT(aParti || CanonicalizeXPCOMParticipant(static_cast<nsISupports*>(aPtr)) == aPtr,
+             "Suspect nsISupports pointer must be canonical");
+
   mPurpleBuf.Put(aPtr, aParti, aRefCnt);
 }
 
@@ -4009,7 +4005,7 @@ SuspectAfterShutdown(void* aPtr, nsCycleCollectionParticipant* aCp,
   if (aRefCnt->get() == 0) {
     if (!aShouldDelete) {
       // The CC is shut down, so we can't be in the middle of an ICC.
-      CanonicalizeParticipant(&aPtr, &aCp);
+      ToParticipant(aPtr, &aCp);
       aRefCnt->stabilizeForDeletion();
       aCp->DeleteCycleCollectable(aPtr);
     } else {