[turbofan] Introduce dedicated BitcastWordToTagged machine operator.

src/compiler/machine-operator.h

 // Copyright 2013 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_COMPILER_MACHINE_OPERATOR_H_
 #define V8_COMPILER_MACHINE_OPERATOR_H_
 
 #include "src/base/flags.h"
 #include "src/machine-type.h"
 
@@ skipping 202 matching lines @@
   const Operator* Int64Mul();
   const Operator* Int64Div();
   const Operator* Int64Mod();
   const Operator* Int64LessThan();
   const Operator* Int64LessThanOrEqual();
   const Operator* Uint64Div();
   const Operator* Uint64LessThan();
   const Operator* Uint64LessThanOrEqual();
   const Operator* Uint64Mod();
 
+  // This operator reinterprets the bits of a word as tagged pointer.
+  const Operator* BitcastWordToTagged();
+
   // These operators change the representation of numbers while preserving the
   // value of the number. Narrowing operators assume the input is representable
   // in the target type and are *not* defined for other inputs.
   // Use narrowing change operators only when there is a static guarantee that
   // the input value is representable in the target value.
   const Operator* ChangeFloat32ToFloat64();
   const Operator* ChangeFloat64ToInt32();   // narrowing
   const Operator* ChangeFloat64ToUint32();  // narrowing
   const Operator* TruncateFloat64ToUint32();
   const Operator* TruncateFloat32ToInt32();
@@ skipping 149 matching lines @@
 };
 
 
 DEFINE_OPERATORS_FOR_FLAGS(MachineOperatorBuilder::Flags)
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_MACHINE_OPERATOR_H_