Implemented the Word64Popcnt TurboFan operator for x64.

src/compiler/x64/code-generator-x64.cc

 // 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.
 
 #include "src/compiler/code-generator.h"
 
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/osr.h"
@@ skipping 778 matching lines @@
         __ Tzcntq(i.OutputRegister(), i.InputOperand(0));
       }
       break;
     case kX64Tzcnt32:
       if (instr->InputAt(0)->IsRegister()) {
         __ Tzcntl(i.OutputRegister(), i.InputRegister(0));
       } else {
         __ Tzcntl(i.OutputRegister(), i.InputOperand(0));
       }
       break;
+    case kX64Popcnt:
+      if (instr->InputAt(0)->IsRegister()) {
+        __ Popcntq(i.OutputRegister(), i.InputRegister(0));
+      } else {
+        __ Popcntq(i.OutputRegister(), i.InputOperand(0));
+      }
+      break;
     case kX64Popcnt32:
       if (instr->InputAt(0)->IsRegister()) {
         __ Popcntl(i.OutputRegister(), i.InputRegister(0));
       } else {
         __ Popcntl(i.OutputRegister(), i.InputOperand(0));
       }
       break;
     case kSSEFloat32Cmp:
       ASSEMBLE_SSE_BINOP(Ucomiss);
       break;
@@ skipping 1043 matching lines @@
     int padding_size = last_lazy_deopt_pc_ + space_needed - current_pc;
     __ Nop(padding_size);
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8