Use signaling NaN for holes in fixed double arrays.

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 638 matching lines @@
   FUNCTION_SCOPE,  // The top-level scope for a function.
   MODULE_SCOPE,    // The scope introduced by a module literal
   SCRIPT_SCOPE,    // The top-level scope for a script or a top-level eval.
   CATCH_SCOPE,     // The scope introduced by catch.
   BLOCK_SCOPE,     // The scope introduced by a new block.
   WITH_SCOPE,      // The scope introduced by with.
   ARROW_SCOPE      // The top-level scope for an arrow function literal.
 };
 
 
-const uint32_t kHoleNanUpper32 = 0x7FFFFFFF;
-const uint32_t kHoleNanLower32 = 0xFFFFFFFF;
-const uint32_t kNaNOrInfinityLowerBoundUpper32 = 0x7FF00000;
+const uint32_t kHoleNanUpper32 = 0x7FF00000;
+const uint32_t kHoleNanLower32 = 0x7FF00000;
 
 const uint64_t kHoleNanInt64 =
     (static_cast<uint64_t>(kHoleNanUpper32) << 32) | kHoleNanLower32;
-const uint64_t kLastNonNaNInt64 =
-    (static_cast<uint64_t>(kNaNOrInfinityLowerBoundUpper32) << 32);
 
 
 // The order of this enum has to be kept in sync with the predicates below.
 enum VariableMode {
   // User declared variables:
   VAR,             // declared via 'var', and 'function' declarations
 
   CONST_LEGACY,    // declared via legacy 'const' declarations
 
   LET,             // declared via 'let' declarations (first lexical)
@@ skipping 140 matching lines @@
   DCHECK(IsValidFunctionKind(kind));
   return kind & FunctionKind::kDefaultConstructor;
 }
 
 
 } }  // namespace v8::internal
 
 namespace i = v8::internal;
 
 #endif  // V8_GLOBALS_H_