Reland "In-object double fields unboxing (for 64-bit only)."

src/heap/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 2735 matching lines @@
                                          int size, AllocationSpace dest) {
   Address dst_addr = dst->address();
   Address src_addr = src->address();
   DCHECK(heap()->AllowedToBeMigrated(src, dest));
   DCHECK(dest != LO_SPACE && size <= Page::kMaxRegularHeapObjectSize);
   if (dest == OLD_POINTER_SPACE) {
     Address src_slot = src_addr;
     Address dst_slot = dst_addr;
     DCHECK(IsAligned(size, kPointerSize));
 
+    bool may_contain_raw_values = src->MayContainRawValues();
+#if V8_DOUBLE_FIELDS_UNBOXING
+    InobjectPropertiesHelper helper(src->map());
+    bool has_only_tagged_fields = helper.all_fields_tagged();
+#endif
     for (int remaining = size / kPointerSize; remaining > 0; remaining--) {
       Object* value = Memory::Object_at(src_slot);
 
       Memory::Object_at(dst_slot) = value;
 
-      if (!src->MayContainRawValues()) {
+#if V8_DOUBLE_FIELDS_UNBOXING
+      if (!may_contain_raw_values &&
+          (has_only_tagged_fields || helper.IsTagged(src_slot - src_addr)))
+#else
+      if (!may_contain_raw_values)
+#endif
+      {
         RecordMigratedSlot(value, dst_slot);
       }
 
       src_slot += kPointerSize;
       dst_slot += kPointerSize;
     }
 
     if (compacting_ && dst->IsJSFunction()) {
       Address code_entry_slot = dst_addr + JSFunction::kCodeEntryOffset;
       Address code_entry = Memory::Address_at(code_entry_slot);
@@ skipping 1620 matching lines @@
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 }
 }  // namespace v8::internal