Reland of Remove slots that point to unboxed doubles from the StoreBuffer/SlotsBuffer.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index e7ffc19fd950c89eaa516afc61938201886f67da..29cf00e9757922789a908ccf24080fd296db8636 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -721,6 +721,7 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
 
   int count = 0;
   int fragmentation = 0;
+  int page_number = 0;
   Candidate* least = NULL;
 
   PageIterator it(space);
@@ -735,9 +736,16 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
     CHECK(p->slots_buffer() == NULL);
 
     if (FLAG_stress_compaction) {
-      unsigned int counter = space->heap()->ms_count();
-      uintptr_t page_number = reinterpret_cast<uintptr_t>(p) >> kPageSizeBits;
-      if ((counter & 1) == (page_number & 1)) fragmentation = 1;
+      if (FLAG_manual_evacuation_candidates_selection) {
+        if (p->IsFlagSet(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING)) {
+          p->ClearFlag(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING);
+          fragmentation = 1;
+        }
+      } else {
+        unsigned int counter = space->heap()->ms_count();
+        if ((counter & 1) == (page_number & 1)) fragmentation = 1;
+        page_number++;
+      }
     } else if (mode == REDUCE_MEMORY_FOOTPRINT) {
       // Don't try to release too many pages.
       if (estimated_release >= over_reserved) {
@@ -4499,6 +4507,21 @@ bool SlotsBuffer::AddTo(SlotsBufferAllocator* allocator,
 }
 
 
+static Object* g_smi_slot = NULL;
+
+
+void SlotsBuffer::RemoveSlot(SlotsBuffer* buffer, ObjectSlot slot_to_remove) {
+  DCHECK_EQ(Smi::FromInt(0), g_smi_slot);
+  DCHECK(!IsTypedSlot(slot_to_remove));
+  while (buffer != NULL) {
+    ObjectSlot* slots = buffer->slots_;
+    // Remove entries by replacing them with a dummy slot containing a smi.
+    std::replace(&slots[0], &slots[buffer->idx_], slot_to_remove, &g_smi_slot);
+    buffer = buffer->next_;
+  }
+}
+
+
 static inline SlotsBuffer::SlotType SlotTypeForRMode(RelocInfo::Mode rmode) {
   if (RelocInfo::IsCodeTarget(rmode)) {
     return SlotsBuffer::CODE_TARGET_SLOT;