Implemented the ctz Turbo Fan operator for x64.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index 08121bda0cd944507fd123633bf9288c7518cc9d..e77b005ea2a0d41b085b4413f3d166c0e708194f 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -584,6 +584,12 @@ void InstructionSelector::VisitWord32Clz(Node* node) {
 }
 
 
+void InstructionSelector::VisitWord64Ctz(Node* node) {
+  X64OperandGenerator g(this);
+  Emit(kX64Tzcnt, g.DefineAsRegister(node), g.Use(node->InputAt(0)));
+}
+
+
 void InstructionSelector::VisitWord32Ctz(Node* node) {
   X64OperandGenerator g(this);
   Emit(kX64Tzcnt32, g.DefineAsRegister(node), g.Use(node->InputAt(0)));
@@ -1606,7 +1612,7 @@ InstructionSelector::SupportedMachineOperatorFlags() {
       MachineOperatorBuilder::kFloat64Max |
       MachineOperatorBuilder::kFloat64Min |
       MachineOperatorBuilder::kWord32ShiftIsSafe |
-      MachineOperatorBuilder::kWord32Ctz;
+      MachineOperatorBuilder::kWord32Ctz | MachineOperatorBuilder::kWord64Ctz;
   if (CpuFeatures::IsSupported(POPCNT)) {
     flags |= MachineOperatorBuilder::kWord32Popcnt;
   }