Do not call Heap::IterateAndMarkPointersToFromSpace() for unboxed double fields.

src/heap/heap.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/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 1782 matching lines @@
       while (!promotion_queue()->is_empty()) {
         HeapObject* target;
         int size;
         promotion_queue()->remove(&target, &size);
 
         // Promoted object might be already partially visited
         // during old space pointer iteration. Thus we search specificly
         // for pointers to from semispace instead of looking for pointers
         // to new space.
         DCHECK(!target->IsMap());
-        IterateAndMarkPointersToFromSpace(
-            target->address(), target->address() + size, &ScavengeObject);
+        Address start_address = target->address();
+        Address end_address = start_address + size;
+#if V8_DOUBLE_FIELDS_UNBOXING
+        InobjectPropertiesHelper helper(target->map());
+        bool has_only_tagged_fields = helper.all_fields_tagged();
+
+        if (!has_only_tagged_fields) {
+          for (Address slot = start_address; slot < end_address;
+               slot += kPointerSize) {
+            if (helper.IsTagged(static_cast<int>(slot - start_address))) {
+              // TODO(ishell): call this once for contiguous region
+              // of tagged fields.
+              IterateAndMarkPointersToFromSpace(slot, slot + kPointerSize,
+                                                &ScavengeObject);
+            }
+          }
+        } else {
+#endif
+          IterateAndMarkPointersToFromSpace(start_address, end_address,
+                                            &ScavengeObject);
+#if V8_DOUBLE_FIELDS_UNBOXING
+        }
+#endif
       }
     }
 
     // Take another spin if there are now unswept objects in new space
     // (there are currently no more unswept promoted objects).
   } while (new_space_front != new_space_.top());
 
   return new_space_front;
 }
 
@@ skipping 4532 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 }
 }  // namespace v8::internal