[turbofan] Introduce dedicated BitcastWordToTagged machine operator.

src/compiler/code-assembler.h

 // 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.
 
 #ifndef V8_COMPILER_CODE_ASSEMBLER_H_
 #define V8_COMPILER_CODE_ASSEMBLER_H_
 
 #include <map>
 
 // Clients of this interface shouldn't depend on lots of compiler internals.
@@ skipping 89 matching lines @@
   V(Word64Xor)                             \
   V(Word64Shr)                             \
   V(Word64Sar)                             \
   V(Word64Ror)
 
 #define CODE_ASSEMBLER_UNARY_OP_LIST(V) \
   V(Float64Neg)                         \
   V(Float64Sqrt)                        \
   V(Float64ExtractLowWord32)            \
   V(Float64ExtractHighWord32)           \
+  V(BitcastWordToTagged)                \
   V(TruncateInt64ToInt32)               \
   V(ChangeFloat64ToUint32)              \
   V(ChangeInt32ToFloat64)               \
   V(ChangeInt32ToInt64)                 \
   V(ChangeUint32ToFloat64)              \
   V(ChangeUint32ToUint64)               \
   V(Float64RoundDown)                   \
   V(Float64RoundUp)                     \
   V(Float64RoundTruncate)               \
   V(Word32Clz)
@@ skipping 262 matching lines @@
   // Map of variables to the list of value nodes that have been added from each
   // merge path in their order of merging.
   std::map<Variable::Impl*, std::vector<Node*>> variable_merges_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_CODE_ASSEMBLER_H_