Debug garbage collector does not correctly remove cross-gen garbage

runtime/vm/gc_marker.cc

Index: runtime/vm/gc_marker.cc
diff --git a/runtime/vm/gc_marker.cc b/runtime/vm/gc_marker.cc
index ef11a9467867e676bc1d7dc75e407f3d6953d8be..6b6971bfa53104ca13ceaace097a02d3a7402333 100644
--- a/runtime/vm/gc_marker.cc
+++ b/runtime/vm/gc_marker.cc
@@ -191,7 +191,11 @@ class MarkingVisitorBase : public ObjectPointerVisitor {
 
         // The key is marked so we make sure to properly visit all pointers
         // originating from this weak property.
-        VisitingOldObject(cur_weak);
+        if (cur_weak->IsOldObject()) {
+          VisitingOldObject(cur_weak);
+        } else {
+          VisitingOldObject(NULL);
+        }
         cur_weak->VisitPointersNonvirtual(this);
       } else {
         // Requeue this weak property to be handled later.
@@ -217,7 +221,12 @@ class MarkingVisitorBase : public ObjectPointerVisitor {
     do {
       do {
         // First drain the marking stacks.
-        VisitingOldObject(raw_obj);
+        if (raw_obj->IsOldObject()) {
+          VisitingOldObject(raw_obj);
+        } else {
+          VisitingOldObject(NULL);
+        }
+
         const intptr_t class_id = raw_obj->GetClassId();
         if (class_id != kWeakPropertyCid) {
           marked_bytes_ += raw_obj->VisitPointersNonvirtual(this);
@@ -306,7 +315,8 @@ class MarkingVisitorBase : public ObjectPointerVisitor {
   void PushMarked(RawObject* raw_obj) {
     ASSERT(raw_obj->IsHeapObject());
     ASSERT((FLAG_verify_gc_contains)
-               ? page_space_->Contains(RawObject::ToAddr(raw_obj))
+               ? ((page_space_->Contains(RawObject::ToAddr(raw_obj))) ||
+                  (heap_->new_space()->Contains(RawObject::ToAddr(raw_obj))))
                : true);
 
     // Push the marked object on the marking stack.
@@ -335,6 +345,9 @@ class MarkingVisitorBase : public ObjectPointerVisitor {
 
     // Fast exit if the raw object is marked.
     if (raw_obj->IsMarked()) {
+      if (raw_obj->IsNewObject()) {
+        ProcessNewSpaceObject(raw_obj, p);
+      }
       return;
     }
 
@@ -346,7 +359,6 @@ class MarkingVisitorBase : public ObjectPointerVisitor {
     // ...
     if (raw_obj->IsNewObject()) {
       ProcessNewSpaceObject(raw_obj, p);
-      return;
     }
 
     if (!TryAcquireMarkBit(raw_obj)) {
@@ -472,9 +484,6 @@ void GCMarker::IterateRoots(Isolate* isolate,
     isolate->VisitObjectPointers(visitor,
                                  StackFrameIterator::kDontValidateFrames);
   }
-  if ((slice_index == 1) || (num_slices <= 1)) {
-    heap_->new_space()->VisitObjectPointers(visitor);
-  }
 
   // For now, we just distinguish two parts of the root set, so any remaining
   // slices are empty.