Access double fields in C++ as uint64_t fields to preserve signaling bit of a NaN.

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 3675 matching lines @@
   // Copy (real) inobject properties. If necessary, stop at number_of_fields to
   // avoid overwriting |one_pointer_filler_map|.
   int limit = Min(inobject, number_of_fields);
   for (int i = 0; i < limit; i++) {
     FieldIndex index = FieldIndex::ForPropertyIndex(*new_map, i);
     Object* value = array->get(external + i);
     // Can't use JSObject::FastPropertyAtPut() because proper map was not set
     // yet.
     if (new_map->IsUnboxedDoubleField(index)) {
       DCHECK(value->IsMutableHeapNumber());
-      object->RawFastDoublePropertyAtPut(index,
-                                         HeapNumber::cast(value)->value());
+      // Ensure that all bits of the double value are preserved.
+      object->RawFastDoublePropertyAsBitsAtPut(
+          index, HeapNumber::cast(value)->value_as_bits());
       if (i < old_number_of_fields && !old_map->IsUnboxedDoubleField(index)) {
         // Transition from tagged to untagged slot.
         heap->ClearRecordedSlot(*object,
                                 HeapObject::RawField(*object, index.offset()));
       } else {
         DCHECK(!heap->HasRecordedSlot(
             *object, HeapObject::RawField(*object, index.offset())));
       }
     } else {
       object->RawFastPropertyAtPut(index, value);
@@ skipping 4234 matching lines @@
     if (copy->HasFastProperties()) {
       Handle<DescriptorArray> descriptors(copy->map()->instance_descriptors());
       int limit = copy->map()->NumberOfOwnDescriptors();
       for (int i = 0; i < limit; i++) {
         PropertyDetails details = descriptors->GetDetails(i);
         if (details.location() != kField) continue;
         DCHECK_EQ(kData, details.kind());
         FieldIndex index = FieldIndex::ForDescriptor(copy->map(), i);
         if (object->IsUnboxedDoubleField(index)) {
           if (copying) {
-            double value = object->RawFastDoublePropertyAt(index);
-            copy->RawFastDoublePropertyAtPut(index, value);
+            // Ensure that all bits of the double value are preserved.
+            uint64_t value = object->RawFastDoublePropertyAsBitsAt(index);
+            copy->RawFastDoublePropertyAsBitsAtPut(index, value);
           }
         } else {
           Handle<Object> value(object->RawFastPropertyAt(index), isolate);
           if (value->IsJSObject()) {
             ASSIGN_RETURN_ON_EXCEPTION(
                 isolate, value,
                 VisitElementOrProperty(copy, Handle<JSObject>::cast(value)),
                 JSObject);
             if (copying) {
               copy->FastPropertyAtPut(index, *value);
@@ skipping 12100 matching lines @@
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 
 }  // namespace internal
 }  // namespace v8