Bug 1167452 - Set gcLastSweepGroupIndex earlier (debugging feature) r=jonco

Differential Revision: https://phabricator.services.mozilla.com/D31951

--HG--
extra : moz-landing-system : lando

js/src/gc/GC.cpp

@@ -5081,10 +5081,13 @@ void GCRuntime::groupZonesForSweeping(JS::GCReason reason) {
   }
 
 #ifdef DEBUG
+  unsigned idx = sweepGroupIndex;
   for (Zone* head = currentSweepGroup; head; head = head->nextGroup()) {
     for (Zone* zone = head; zone; zone = zone->nextNodeInGroup()) {
       MOZ_ASSERT(zone->isGCMarking());
+      zone->gcSweepGroupIndex = idx;
     }
+    idx++;
   }
 
   MOZ_ASSERT_IF(!isIncremental, !currentSweepGroup->nextGroup());
@@ -5761,10 +5764,6 @@ IncrementalProgress GCRuntime::beginSweepingSweepGroup(FreeOp* fop,
     if (zone->isAtomsZone()) {
       sweepingAtoms = true;
     }
-
-#ifdef DEBUG
-    zone->gcLastSweepGroupIndex = sweepGroupIndex;
-#endif
   }
 
   validateIncrementalMarking();
@@ -7109,6 +7108,12 @@ void GCRuntime::incrementalSlice(SliceBudget& budget, JS::GCReason reason,
       MOZ_ASSERT(!lastMarkSlice);
       rootsRemoved = false;
 
+#ifdef DEBUG
+      for (ZonesIter zone(rt, WithAtoms); !zone.done(); zone.next()) {
+        zone->gcSweepGroupIndex = 0;
+      }
+#endif
+
       incrementalState = State::MarkRoots;
 
       MOZ_FALLTHROUGH;

js/src/gc/Zone.cpp

@@ -63,7 +63,7 @@ JS::Zone::Zone(JSRuntime* rt)
       data(this, nullptr),
       isSystem(this, false),
 #ifdef DEBUG
-      gcLastSweepGroupIndex(0),
+      gcSweepGroupIndex(0),
 #endif
       jitZone_(this, nullptr),
       gcScheduled_(false),

js/src/gc/Zone.h

@@ -301,7 +301,7 @@ class Zone : public JS::shadow::Zone,
 
   // For testing purposes, return the index of the sweep group which this zone
   // was swept in in the last GC.
-  unsigned lastSweepGroupIndex() { return gcLastSweepGroupIndex; }
+  unsigned lastSweepGroupIndex() { return gcSweepGroupIndex; }
 #endif
 
   void sweepBreakpoints(js::FreeOp* fop);
@@ -625,7 +625,7 @@ class Zone : public JS::shadow::Zone,
   js::ZoneData<bool> isSystem;
 
 #ifdef DEBUG
-  js::MainThreadData<unsigned> gcLastSweepGroupIndex;
+  js::MainThreadData<unsigned> gcSweepGroupIndex;
 #endif
 
   static js::HashNumber UniqueIdToHash(uint64_t uid);