Bug 986843 - Don't sweep empty zones if they contain marked compartments r=terrence

js/src/gc/Zone.cpp

@@ -258,4 +258,12 @@ js::ZoneOfObjectFromAnyThread(const JSObject &obj)
     return obj.zoneFromAnyThread();
 }
 
-
+bool
+Zone::hasMarkedCompartments()
+{
+    for (CompartmentsInZoneIter comp(this); !comp.done(); comp.next()) {
+        if (comp->marked)
+            return true;
+    }
+    return false;
+}

js/src/gc/Zone.h

@@ -317,6 +317,8 @@ struct Zone : public JS::shadow::Zone,
 
     void sweep(js::FreeOp *fop, bool releaseTypes);
 
+    bool hasMarkedCompartments();
+
   private:
     void sweepBreakpoints(js::FreeOp *fop);
 

js/src/jsgc.cpp

@@ -2864,7 +2864,9 @@ SweepZones(FreeOp *fop, bool lastGC)
         Zone *zone = *read++;
 
         if (zone->wasGCStarted()) {
-            if (zone->allocator.arenas.arenaListsAreEmpty() || lastGC) {
+            if ((zone->allocator.arenas.arenaListsAreEmpty() && !zone->hasMarkedCompartments()) ||
+                lastGC)
+            {
                 zone->allocator.arenas.checkEmptyFreeLists();
                 if (callback)
                     callback(zone);