Implemented the Word64Popcnt TurboFan operator for x64.

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index ea92ae0aa3e9302d7879a277cd73a944aa07a427..9d71935b192cba1bd57fd25a12d9c5fb17745658 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -120,10 +120,11 @@ class MachineOperatorBuilder final : public ZoneObject {
     kWord32Ctz = 1u << 10,
     kWord32Popcnt = 1u << 11,
     kWord64Ctz = 1u << 12,
+    kWord64Popcnt = 1u << 13,
     kAllOptionalOps = kFloat32Max | kFloat32Min | kFloat64Max | kFloat64Min |
                       kFloat64RoundDown | kFloat64RoundTruncate |
                       kFloat64RoundTiesAway | kWord32Ctz | kWord32Popcnt |
-                      kWord64Ctz
+                      kWord64Ctz | kWord64Popcnt
   };
   typedef base::Flags<Flag, unsigned> Flags;
 
@@ -141,6 +142,7 @@ class MachineOperatorBuilder final : public ZoneObject {
   const Operator* Word32Clz();
   const OptionalOperator Word32Ctz();
   const OptionalOperator Word32Popcnt();
+  const OptionalOperator Word64Popcnt();
   bool Word32ShiftIsSafe() const { return flags_ & kWord32ShiftIsSafe; }
 
   const Operator* Word64And();