[heap] delete Heap::LeftTrimFixedAray

No more uses left for this code (thank goodness.)

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1474693003

Cr-Commit-Position: refs/heads/master@{#32305}

src/flag-definitions.h

@@ -696,7 +696,6 @@ DEFINE_IMPLICATION(trace_detached_contexts, track_detached_contexts)
 #ifdef VERIFY_HEAP
 DEFINE_BOOL(verify_heap, false, "verify heap pointers before and after GC")
 #endif
-DEFINE_BOOL(move_object_start, false, "enable moving of object starts")
 DEFINE_BOOL(memory_reducer, true, "use memory reducer")
 DEFINE_BOOL(scavenge_reclaim_unmodified_objects, false,
             "remove unmodified and unreferenced objects")

src/heap/heap.cc

@@ -3066,24 +3066,6 @@ void Heap::CreateFillerObjectAt(Address addr, int size) {
 }
 
 
-bool Heap::CanMoveObjectStart(HeapObject* object) {
-  if (!FLAG_move_object_start) return false;
-
-  Address address = object->address();
-
-  if (lo_space()->Contains(object)) return false;
-
-  Page* page = Page::FromAddress(address);
-  // We can move the object start if:
-  // (1) the object is not in old space,
-  // (2) the page of the object was already swept,
-  // (3) the page was already concurrently swept. This case is an optimization
-  // for concurrent sweeping. The WasSwept predicate for concurrently swept
-  // pages is set after sweeping all pages.
-  return !InOldSpace(address) || page->WasSwept() || page->SweepingCompleted();
-}
-
-
 void Heap::AdjustLiveBytes(HeapObject* object, int by, InvocationMode mode) {
   if (incremental_marking()->IsMarking() &&
       Marking::IsBlack(Marking::MarkBitFrom(object->address()))) {
@@ -3096,55 +3078,6 @@ void Heap::AdjustLiveBytes(HeapObject* object, int by, InvocationMode mode) {
 }
 
 
-FixedArrayBase* Heap::LeftTrimFixedArray(FixedArrayBase* object,
-                                         int elements_to_trim) {
-  DCHECK(!object->IsFixedTypedArrayBase());
-  const int element_size = object->IsFixedArray() ? kPointerSize : kDoubleSize;
-  const int bytes_to_trim = elements_to_trim * element_size;
-  Map* map = object->map();
-
-  // For now this trick is only applied to objects in new and paged space.
-  // In large object space the object's start must coincide with chunk
-  // and thus the trick is just not applicable.
-  DCHECK(!lo_space()->Contains(object));
-  DCHECK(object->map() != fixed_cow_array_map());
-
-  STATIC_ASSERT(FixedArrayBase::kMapOffset == 0);
-  STATIC_ASSERT(FixedArrayBase::kLengthOffset == kPointerSize);
-  STATIC_ASSERT(FixedArrayBase::kHeaderSize == 2 * kPointerSize);
-
-  const int len = object->length();
-  DCHECK(elements_to_trim <= len);
-
-  // Calculate location of new array start.
-  Address new_start = object->address() + bytes_to_trim;
-
-  // Technically in new space this write might be omitted (except for
-  // debug mode which iterates through the heap), but to play safer
-  // we still do it.
-  CreateFillerObjectAt(object->address(), bytes_to_trim);
-
-  // Initialize header of the trimmed array. Since left trimming is only
-  // performed on pages which are not concurrently swept creating a filler
-  // object does not require synchronization.
-  DCHECK(CanMoveObjectStart(object));
-  Object** former_start = HeapObject::RawField(object, 0);
-  int new_start_index = elements_to_trim * (element_size / kPointerSize);
-  former_start[new_start_index] = map;
-  former_start[new_start_index + 1] = Smi::FromInt(len - elements_to_trim);
-  FixedArrayBase* new_object =
-      FixedArrayBase::cast(HeapObject::FromAddress(new_start));
-
-  // Maintain consistency of live bytes during incremental marking
-  Marking::TransferMark(this, object->address(), new_start);
-  AdjustLiveBytes(new_object, -bytes_to_trim, Heap::CONCURRENT_TO_SWEEPER);
-
-  // Notify the heap profiler of change in object layout.
-  OnMoveEvent(new_object, object, new_object->Size());
-  return new_object;
-}
-
-
 // Force instantiation of templatized method.
 template void Heap::RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(
     FixedArrayBase*, int);

src/heap/heap.h

@@ -827,15 +827,9 @@ class Heap {
   // when introducing gaps within pages.
   void CreateFillerObjectAt(Address addr, int size);
 
-  bool CanMoveObjectStart(HeapObject* object);
-
   // Maintain consistency of live bytes during incremental marking.
   void AdjustLiveBytes(HeapObject* object, int by, InvocationMode mode);
 
-  // Trim the given array from the left. Note that this relocates the object
-  // start and hence is only valid if there is only a single reference to it.
-  FixedArrayBase* LeftTrimFixedArray(FixedArrayBase* obj, int elements_to_trim);
-
   // Trim the given array from the right.
   template<Heap::InvocationMode mode>
   void RightTrimFixedArray(FixedArrayBase* obj, int elements_to_trim);

src/heap/mark-compact.cc

@@ -594,43 +594,6 @@ bool MarkCompactCollector::IsSweepingCompleted() {
 }
 
 
-void Marking::TransferMark(Heap* heap, Address old_start, Address new_start) {
-  // This is only used when resizing an object.
-  DCHECK(MemoryChunk::FromAddress(old_start) ==
-         MemoryChunk::FromAddress(new_start));
-
-  if (!heap->incremental_marking()->IsMarking()) return;
-
-  // If the mark doesn't move, we don't check the color of the object.
-  // It doesn't matter whether the object is black, since it hasn't changed
-  // size, so the adjustment to the live data count will be zero anyway.
-  if (old_start == new_start) return;
-
-  MarkBit new_mark_bit = MarkBitFrom(new_start);
-  MarkBit old_mark_bit = MarkBitFrom(old_start);
-
-#ifdef DEBUG
-  ObjectColor old_color = Color(old_mark_bit);
-#endif
-
-  if (Marking::IsBlack(old_mark_bit)) {
-    Marking::BlackToWhite(old_mark_bit);
-    Marking::MarkBlack(new_mark_bit);
-    return;
-  } else if (Marking::IsGrey(old_mark_bit)) {
-    Marking::GreyToWhite(old_mark_bit);
-    heap->incremental_marking()->WhiteToGreyAndPush(
-        HeapObject::FromAddress(new_start), new_mark_bit);
-    heap->incremental_marking()->RestartIfNotMarking();
-  }
-
-#ifdef DEBUG
-  ObjectColor new_color = Color(new_mark_bit);
-  DCHECK(new_color == old_color);
-#endif
-}
-
-
 const char* AllocationSpaceName(AllocationSpace space) {
   switch (space) {
     case NEW_SPACE:

src/heap/mark-compact.h

@@ -119,8 +119,6 @@ class Marking : public AllStatic {
     markbit.Next().Set();
   }
 
-  static void TransferMark(Heap* heap, Address old_start, Address new_start);
-
 #ifdef DEBUG
   enum ObjectColor {
     BLACK_OBJECT,