Version 5.2.361.32 (cherry-pick)

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index cbc6d72ad839a31822e64cbd93df6503ccca5133..c8f1557c31b6c83ff2bad45c653afe7e442ac4c5 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -3117,10 +3117,6 @@ FixedArrayBase* Heap::LeftTrimFixedArray(FixedArrayBase* object,
   DCHECK(!lo_space()->Contains(object));
   DCHECK(object->map() != fixed_cow_array_map());
 
-  // Ensure that the no handle-scope has more than one pointer to the same
-  // backing-store.
-  SLOW_DCHECK(CountHandlesForObject(object) <= 1);
-
   STATIC_ASSERT(FixedArrayBase::kMapOffset == 0);
   STATIC_ASSERT(FixedArrayBase::kLengthOffset == kPointerSize);
   STATIC_ASSERT(FixedArrayBase::kHeaderSize == 2 * kPointerSize);
@@ -4763,6 +4759,49 @@ void Heap::IterateSmiRoots(ObjectVisitor* v) {
   v->Synchronize(VisitorSynchronization::kSmiRootList);
 }
 
+// We cannot avoid stale handles to left-trimmed objects, but can only make
+// sure all handles still needed are updated. Filter out a stale pointer
+// and clear the slot to allow post processing of handles (needed because
+// the sweeper might actually free the underlying page).
+class FixStaleLeftTrimmedHandlesVisitor : public ObjectVisitor {
+ public:
+  explicit FixStaleLeftTrimmedHandlesVisitor(Heap* heap) : heap_(heap) {
+    USE(heap_);
+  }
+
+  void VisitPointer(Object** p) override { FixHandle(p); }
+
+  void VisitPointers(Object** start, Object** end) override {
+    for (Object** p = start; p < end; p++) FixHandle(p);
+  }
+
+ private:
+  inline void FixHandle(Object** p) {
+    HeapObject* current = reinterpret_cast<HeapObject*>(*p);
+    if (!current->IsHeapObject()) return;
+    const MapWord map_word = current->map_word();
+    if (!map_word.IsForwardingAddress() && current->IsFiller()) {
+#ifdef DEBUG
+      // We need to find a FixedArrayBase map after walking the fillers.
+      while (current->IsFiller()) {
+        Address next = reinterpret_cast<Address>(current);
+        if (current->map() == heap_->one_pointer_filler_map()) {
+          next += kPointerSize;
+        } else if (current->map() == heap_->two_pointer_filler_map()) {
+          next += 2 * kPointerSize;
+        } else {
+          next += current->Size();
+        }
+        current = reinterpret_cast<HeapObject*>(next);
+      }
+      DCHECK(current->IsFixedArrayBase());
+#endif  // DEBUG
+      *p = nullptr;
+    }
+  }
+
+  Heap* heap_;
+};
 
 void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
   v->VisitPointers(&roots_[0], &roots_[kStrongRootListLength]);
@@ -4783,6 +4822,8 @@ void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
   v->Synchronize(VisitorSynchronization::kCompilationCache);
 
   // Iterate over local handles in handle scopes.
+  FixStaleLeftTrimmedHandlesVisitor left_trim_visitor(this);
+  isolate_->handle_scope_implementer()->Iterate(&left_trim_visitor);
   isolate_->handle_scope_implementer()->Iterate(v);
   isolate_->IterateDeferredHandles(v);
   v->Synchronize(VisitorSynchronization::kHandleScope);
@@ -5632,32 +5673,6 @@ void Heap::PrintHandles() {
 
 #endif
 
-#ifdef ENABLE_SLOW_DCHECKS
-
-class CountHandleVisitor : public ObjectVisitor {
- public:
-  explicit CountHandleVisitor(Object* object) : object_(object) {}
-
-  void VisitPointers(Object** start, Object** end) override {
-    for (Object** p = start; p < end; p++) {
-      if (object_ == reinterpret_cast<Object*>(*p)) count_++;
-    }
-  }
-
-  int count() { return count_; }
-
- private:
-  Object* object_;
-  int count_ = 0;
-};
-
-int Heap::CountHandlesForObject(Object* object) {
-  CountHandleVisitor v(object);
-  isolate_->handle_scope_implementer()->Iterate(&v);
-  return v.count();
-}
-#endif
-
 class CheckHandleCountVisitor : public ObjectVisitor {
  public:
   CheckHandleCountVisitor() : handle_count_(0) {}