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

src/factory.h

 // Copyright 2014 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.
 
 #ifndef V8_FACTORY_H_
 #define V8_FACTORY_H_
 
 #include "src/globals.h"
 #include "src/isolate.h"
 #include "src/messages.h"
@@ skipping 419 matching lines @@
   Handle<Object> NewNumberFromInt64(int64_t value,
                                     PretenureFlag pretenure = NOT_TENURED) {
     if (value <= std::numeric_limits<int32_t>::max() &&
         value >= std::numeric_limits<int32_t>::min() &&
         Smi::IsValid(static_cast<int32_t>(value))) {
       return Handle<Object>(Smi::FromInt(static_cast<int32_t>(value)),
                             isolate());
     }
     return NewNumber(static_cast<double>(value), pretenure);
   }
-  Handle<HeapNumber> NewHeapNumber(double value,
-                                   MutableMode mode = IMMUTABLE,
-                                   PretenureFlag pretenure = NOT_TENURED);
-
+  Handle<HeapNumber> NewHeapNumber(double value, MutableMode mode = IMMUTABLE,
+                                   PretenureFlag pretenure = NOT_TENURED) {
+    Handle<HeapNumber> heap_number = NewHeapNumber(mode, pretenure);
+    heap_number->set_value(value);
+    return heap_number;
+  }
+  // Creates mutable heap number object with value field set to hole NaN.
   Handle<HeapNumber> NewMutableHeapNumber(
       PretenureFlag pretenure = NOT_TENURED) {
-    double hole_nan = bit_cast<double>(kHoleNanInt64);
-    return NewHeapNumber(hole_nan, MUTABLE, pretenure);
+    Handle<HeapNumber> heap_number = NewHeapNumber(MUTABLE, pretenure);
+    heap_number->set_value_as_bits(kHoleNanInt64);
+    return heap_number;
   }
 
+  // Creates heap number object with not yet set value field.
+  Handle<HeapNumber> NewHeapNumber(MutableMode mode,
+                                   PretenureFlag pretenure = NOT_TENURED);
+
 #define SIMD128_NEW_DECL(TYPE, Type, type, lane_count, lane_type) \
   Handle<Type> New##Type(lane_type lanes[lane_count],             \
                          PretenureFlag pretenure = NOT_TENURED);
   SIMD128_TYPES(SIMD128_NEW_DECL)
 #undef SIMD128_NEW_DECL
 
   Handle<JSWeakMap> NewJSWeakMap();
 
   Handle<JSObject> NewArgumentsObject(Handle<JSFunction> callee, int length);
 
@@ skipping 362 matching lines @@
   void SetStrictFunctionInstanceDescriptor(Handle<Map> map,
                                            FunctionMode function_mode);
 
   void SetClassFunctionInstanceDescriptor(Handle<Map> map);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_FACTORY_H_