Use a tag bit for indicating prologue weak persistent handles, this avoids

runtime/vm/handles_impl.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_HANDLES_IMPL_H_
 #define VM_HANDLES_IMPL_H_
 
 #include "vm/heap.h"
 #include "vm/visitor.h"
 
@@ skipping 31 matching lines @@
     }
     block = block->next_block();
   } while (block != NULL);
   UNREACHABLE();
 }
 
 
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 void Handles<kHandleSizeInWords,
              kHandlesPerChunk,
-             kOffsetOfRawPtr>::Visit(HandleVisitor* visitor) {
+             kOffsetOfRawPtr>::Visit(HandleVisitor* visitor,
+                                     bool is_prologue_weak) {
   // Visit all zone handles.
   HandlesBlock* block = zone_blocks_;
   while (block != NULL) {
-    block->Visit(visitor);
+    block->Visit(visitor, is_prologue_weak);
     block = block->next_block();
   }
 
   // Visit all scoped handles.
   block = &first_scoped_block_;
   do {
-    block->Visit(visitor);
+    block->Visit(visitor, is_prologue_weak);
     block = block->next_block();
   } while (block != NULL);
 }
 
 
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 void Handles<kHandleSizeInWords,
              kHandlesPerChunk,
              kOffsetOfRawPtr>::Reset() {
   // Delete all the extra zone handle blocks allocated and reinit the first
@@ skipping 260 matching lines @@
   for (intptr_t i = 0; i < next_handle_slot_; i += kHandleSizeInWords) {
     visitor->VisitPointer(
         reinterpret_cast<RawObject**>(&data_[i + kOffsetOfRawPtr/kWordSize]));
   }
 }
 
 
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 void Handles<kHandleSizeInWords,
              kHandlesPerChunk,
-             kOffsetOfRawPtr>::HandlesBlock::Visit(HandleVisitor* visitor) {
+             kOffsetOfRawPtr>::HandlesBlock::Visit(HandleVisitor* visitor,
+                                                   bool is_prologue_weak) {
   ASSERT(visitor != NULL);
   for (intptr_t i = 0; i < next_handle_slot_; i += kHandleSizeInWords) {
-    visitor->VisitHandle(reinterpret_cast<uword>(&data_[i]));
+    visitor->VisitHandle(reinterpret_cast<uword>(&data_[i]), is_prologue_weak);
   }
 }
 
 
 #if defined(DEBUG)
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 void Handles<kHandleSizeInWords,
              kHandlesPerChunk,
              kOffsetOfRawPtr>::HandlesBlock::ZapFreeHandles() {
   // Reinitialize the handle area to some uninitialized value.
   for (intptr_t i = next_handle_slot_;
        i < (kHandleSizeInWords * kHandlesPerChunk);
        i++) {
     data_[i] = kZapUninitializedWord;
   }
 }
 #endif
 
 
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 int Handles<kHandleSizeInWords,
             kHandlesPerChunk,
             kOffsetOfRawPtr>::HandlesBlock::HandleCount() const {
   return (next_handle_slot_ / kHandleSizeInWords);
 }
 
 }  // namespace dart
 
 #endif  // VM_HANDLES_IMPL_H_