MIPS64: Implement the Word64Clz TurboFan operator.

src/compiler/mips64/code-generator-mips64.cc

Index: src/compiler/mips64/code-generator-mips64.cc
diff --git a/src/compiler/mips64/code-generator-mips64.cc b/src/compiler/mips64/code-generator-mips64.cc
index 86d723c68664f33f59b00b35e342a158ad7030b9..24a3fa6ccd899863e94988ee83b14323564134e5 100644
--- a/src/compiler/mips64/code-generator-mips64.cc
+++ b/src/compiler/mips64/code-generator-mips64.cc
@@ -578,6 +578,9 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
     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));