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

src/compiler/mips64/code-generator-mips64.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 "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"
 #include "src/mips/macro-assembler-mips.h"
@@ skipping 560 matching lines @@
       break;
     case kMips64Or:
       __ Or(i.OutputRegister(), i.InputRegister(0), i.InputOperand(1));
       break;
     case kMips64Xor:
       __ Xor(i.OutputRegister(), i.InputRegister(0), i.InputOperand(1));
       break;
     case kMips64Clz:
       __ Clz(i.OutputRegister(), i.InputRegister(0));
       break;
+    case kMips64Dclz:
+      __ dclz(i.OutputRegister(), i.InputRegister(0));
+      break;
     case kMips64Shl:
       if (instr->InputAt(1)->IsRegister()) {
         __ sllv(i.OutputRegister(), i.InputRegister(0), i.InputRegister(1));
       } else {
         int64_t imm = i.InputOperand(1).immediate();
         __ sll(i.OutputRegister(), i.InputRegister(0),
                static_cast<uint16_t>(imm));
       }
       break;
     case kMips64Shr:
@@ skipping 1013 matching lines @@
       padding_size -= v8::internal::Assembler::kInstrSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8