Make memento checks more stable. Add filler at the end of new space and check if object and memento…

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index f8588b87e6eda4763e3f757a8deda15fa47fbd42..a6db39c58cde422c7536d22c2dab95a232a75f9e 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -768,6 +768,18 @@ bool Heap::CollectGarbage(AllocationSpace space,
   allocation_timeout_ = Max(6, FLAG_gc_interval);
 #endif
 
+  // There may be an allocation memento behind every object in new space.
+  // If we evacuate a not full new space or if we are on the last page of
+  // the new space, then there may be uninitialized memory behind the top
+  // pointer of the new space page. We store a filler object there to
+  // identify the unused space.
+  Address from_top = new_space_.top();
+  Address from_limit = new_space_.limit();
+  if (from_top < from_limit) {
+    int remaining_in_page = static_cast<int>(from_limit - from_top);
+    CreateFillerObjectAt(from_top, remaining_in_page);
+  }
+
   if (collector == SCAVENGER && !incremental_marking()->IsStopped()) {
     if (FLAG_trace_incremental_marking) {
       PrintF("[IncrementalMarking] Scavenge during marking.\n");