Implemented the Word64Clz TurboFan operator for x64, arm64, and mips64.

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

 // Copyright 2014 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 <algorithm>
 
 #include "src/base/adapters.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
@@ skipping 554 matching lines @@
 void InstructionSelector::VisitWord32Ror(Node* node) {
   VisitWord32Shift(this, node, kX64Ror32);
 }
 
 
 void InstructionSelector::VisitWord64Ror(Node* node) {
   VisitWord64Shift(this, node, kX64Ror);
 }
 
 
+void InstructionSelector::VisitWord64Clz(Node* node) {
+  X64OperandGenerator g(this);
+  Emit(kX64Lzcnt, g.DefineAsRegister(node), g.Use(node->InputAt(0)));
+}
+
+
 void InstructionSelector::VisitWord32Clz(Node* node) {
   X64OperandGenerator g(this);
   Emit(kX64Lzcnt32, 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)));
 }
@@ skipping 1022 matching lines @@
   if (CpuFeatures::IsSupported(SSE4_1)) {
     flags |= MachineOperatorBuilder::kFloat64RoundDown |
              MachineOperatorBuilder::kFloat64RoundTruncate;
   }
   return flags;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8