Implemented the Word64Popcnt TurboFan operator for x64.

src/x64/macro-assembler-x64.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_X64_MACRO_ASSEMBLER_X64_H_
 #define V8_X64_MACRO_ASSEMBLER_X64_H_
 
 #include "src/assembler.h"
 #include "src/bailout-reason.h"
 #include "src/base/flags.h"
@@ skipping 1007 matching lines @@
 
   void Tzcntq(Register dst, Register src);
   void Tzcntq(Register dst, const Operand& src);
 
   void Tzcntl(Register dst, Register src);
   void Tzcntl(Register dst, const Operand& src);
 
   void Popcntl(Register dst, Register src);
   void Popcntl(Register dst, const Operand& src);
 
+  void Popcntq(Register dst, Register src);
+  void Popcntq(Register dst, const Operand& src);
+
   // Non-x64 instructions.
   // Push/pop all general purpose registers.
   // Does not push rsp/rbp nor any of the assembler's special purpose registers
   // (kScratchRegister, kRootRegister).
   void Pushad();
   void Popad();
   // Sets the stack as after performing Popad, without actually loading the
   // registers.
   void Dropad();
 
@@ skipping 685 matching lines @@
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_