Precise sweeping makes zapping of garbage memory when trimming arrays obsolete

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/439863006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22867 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap/heap.cc

@@ -3260,15 +3260,6 @@ void Heap::AdjustLiveBytes(Address address, int by, InvocationMode mode) {
 }
 
 
-static void ZapFixedArrayForTrimming(Address address, int elements_to_trim) {
-  Object** zap = reinterpret_cast<Object**>(address);
-  zap++;  // Header of filler must be at least one word so skip that.
-  for (int i = 1; i < elements_to_trim; i++) {
-    *zap++ = Smi::FromInt(0);
-  }
-}
-
-
 FixedArrayBase* Heap::LeftTrimFixedArray(FixedArrayBase* object,
                                          int elements_to_trim) {
   const int element_size = object->IsFixedArray() ? kPointerSize : kDoubleSize;
@@ -3291,15 +3282,6 @@ FixedArrayBase* Heap::LeftTrimFixedArray(FixedArrayBase* object,
   // Calculate location of new array start.
   Address new_start = object->address() + bytes_to_trim;
 
-  if (bytes_to_trim > FreeSpace::kHeaderSize &&
-      object->IsFixedArray() &&
-      !new_space()->Contains(object)) {
-    // If we are doing a big trim in old space then we zap the space that was
-    // formerly part of the array so that the GC (aided by the card-based
-    // remembered set) won't find pointers to new-space there.
-    ZapFixedArrayForTrimming(object->address(), elements_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.
@@ -3348,15 +3330,6 @@ void Heap::RightTrimFixedArray(FixedArrayBase* object, int elements_to_trim) {
   // Calculate location of new array end.
   Address new_end = object->address() + object->Size() - bytes_to_trim;
 
-  if (bytes_to_trim > FreeSpace::kHeaderSize &&
-      object->IsFixedArray() &&
-      (mode != Heap::FROM_GC || Heap::ShouldZapGarbage())) {
-    // If we are doing a big trim in old space then we zap the space that was
-    // formerly part of the array so that the GC (aided by the card-based
-    // remembered set) won't find pointers to new-space there.
-    ZapFixedArrayForTrimming(new_end, elements_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.