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

src/globals.h

 // 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.
 
 #ifndef V8_GLOBALS_H_
 #define V8_GLOBALS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 63 matching lines @@
 // stack allocating MacroAssembler takes 120K bytes.
 // See issue crbug.com/405338
 #define V8_DEFAULT_STACK_SIZE_KB 864
 #else
 // Slightly less than 1MB, since Windows' default stack size for
 // the main execution thread is 1MB for both 32 and 64-bit.
 #define V8_DEFAULT_STACK_SIZE_KB 984
 #endif
 
 
+// Determine whether double field unboxing feature is enabled.
+#if (V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64)
+#define V8_DOUBLE_FIELDS_UNBOXING 0
+#else
+#define V8_DOUBLE_FIELDS_UNBOXING 0
+#endif
+
 // Support for alternative bool type. This is only enabled if the code is
 // compiled with USE_MYBOOL defined. This catches some nasty type bugs.
 // For instance, 'bool b = "false";' results in b == true! This is a hidden
 // source of bugs.
 // However, redefining the bool type does have some negative impact on some
 // platforms. It gives rise to compiler warnings (i.e. with
 // MSVC) in the API header files when mixing code that uses the standard
 // bool with code that uses the redefined version.
 // This does not actually belong in the platform code, but needs to be
 // defined here because the platform code uses bool, and platform.h is
@@ skipping 725 matching lines @@
 
 inline bool IsDefaultConstructorCallSuper(FunctionKind kind) {
   DCHECK(IsValidFunctionKind(kind));
   return kind & FunctionKind::kDefaultConstructorCallSuper;
 }
 } }  // namespace v8::internal
 
 namespace i = v8::internal;
 
 #endif  // V8_GLOBALS_H_