Bug 1735296 - Part 6: Add minor sweeping tracer r=sfink

Analagous to the sweeping tracer, this checks whether nursery things have been
moved and updates the edge as necessary.

Differential Revision: https://phabricator.services.mozilla.com/D128262

Author: jonco3

js/public/TracingAPI.h

@@ -44,6 +44,7 @@ enum class TracerKind {
   GrayBuffering,
   ClearEdges,
   Sweeping,
+  MinorSweeping,
   Barrier,
 
   // Callback tracers: General-purpose tracers that have a single virtual

js/src/gc/GCInternals.h

@@ -288,6 +288,16 @@ struct SweepingTracer final : public GenericTracerImpl<SweepingTracer> {
   friend class GenericTracerImpl<SweepingTracer>;
 };
 
+struct MinorSweepingTracer final
+    : public GenericTracerImpl<MinorSweepingTracer> {
+  explicit MinorSweepingTracer(JSRuntime* rt);
+
+ private:
+  template <typename T>
+  T* onEdge(T* thingp);
+  friend class GenericTracerImpl<MinorSweepingTracer>;
+};
+
 extern void DelayCrossCompartmentGrayMarking(JSObject* src);
 
 inline bool IsOOMReason(JS::GCReason reason) {

js/src/gc/Marking.cpp

@@ -179,8 +179,10 @@ void js::CheckTracedThing(JSTracer* trc, T* thing) {
   MOZ_ASSERT(thing);
 
   if (IsForwarded(thing)) {
-    MOZ_ASSERT(IsTracerKind(trc, JS::TracerKind::Moving) ||
-               trc->isTenuringTracer());
+    JS::TracerKind kind = trc->kind();
+    MOZ_ASSERT(kind == JS::TracerKind::Tenuring ||
+               kind == JS::TracerKind::MinorSweeping ||
+               kind == JS::TracerKind::Moving);
     thing = Forwarded(thing);
   }
 

js/src/gc/Nursery.cpp

@@ -1236,7 +1236,7 @@ js::Nursery::CollectionResult js::Nursery::doCollection(JS::GCReason reason) {
   // Sweep to update any pointers to nursery objects that have now been
   // tenured.
   startProfile(ProfileKey::Sweep);
-  sweep(&mover);
+  sweep();
   endProfile(ProfileKey::Sweep);
 
   // Update any slot or element pointers whose destination has been tenured.
@@ -1431,7 +1431,9 @@ bool js::Nursery::registerMallocedBuffer(void* buffer, size_t nbytes) {
   return true;
 }
 
-void js::Nursery::sweep(JSTracer* trc) {
+void js::Nursery::sweep() {
+  MinorSweepingTracer trc(runtime());
+
   // Sweep unique IDs first before we sweep any tables that may be keyed based
   // on them.
   for (Cell* cell : cellsWithUid_) {
@@ -1445,12 +1447,8 @@ void js::Nursery::sweep(JSTracer* trc) {
   }
   cellsWithUid_.clear();
 
-  for (CompartmentsIter c(runtime()); !c.done(); c.next()) {
-    c->sweepAfterMinorGC(trc);
-  }
-
-  for (ZonesIter zone(trc->runtime(), SkipAtoms); !zone.done(); zone.next()) {
-    zone->sweepAfterMinorGC(trc);
+  for (ZonesIter zone(runtime(), SkipAtoms); !zone.done(); zone.next()) {
+    zone->sweepAfterMinorGC(&trc);
   }
 
   sweepMapAndSetObjects();

js/src/gc/Nursery.h

@@ -677,7 +677,7 @@ class Nursery {
 
   // Updates pointers to nursery objects that have been tenured and discards
   // pointers to objects that have been freed.
-  void sweep(JSTracer* trc);
+  void sweep();
 
   // Reset the current chunk and position after a minor collection. Also poison
   // the nursery on debug & nightly builds.

js/src/gc/Tenuring.cpp

@@ -975,3 +975,23 @@ size_t js::TenuringTracer::moveBigIntToTenured(JS::BigInt* dst, JS::BigInt* src,
 
   return size;
 }
+
+MinorSweepingTracer::MinorSweepingTracer(JSRuntime* rt)
+    : GenericTracerImpl(rt, JS::TracerKind::MinorSweeping,
+                        JS::WeakMapTraceAction::TraceKeysAndValues) {
+  MOZ_ASSERT(CurrentThreadCanAccessRuntime(runtime()));
+  MOZ_ASSERT(JS::RuntimeHeapIsMinorCollecting());
+}
+
+template <typename T>
+inline T* MinorSweepingTracer::onEdge(T* thing) {
+  if (thing->isTenured()) {
+    return thing;
+  }
+
+  if (IsForwarded(thing)) {
+    return Forwarded(thing);
+  }
+
+  return nullptr;
+}

js/src/gc/Zone.cpp

@@ -266,6 +266,10 @@ static void SweepEphemeronEdgesWhileMinorSweeping(
 void Zone::sweepAfterMinorGC(JSTracer* trc) {
   sweepEphemeronTablesAfterMinorGC();
   crossZoneStringWrappers().sweepAfterMinorGC(trc);
+
+  for (CompartmentsInZoneIter comp(this); !comp.done(); comp.next()) {
+    comp->sweepAfterMinorGC(trc);
+  }
 }
 
 void Zone::sweepEphemeronTablesAfterMinorGC() {