CTZ instruction implemented as optional operator.

src/compiler/mips64/instruction-selector-mips64.cc

Index: src/compiler/mips64/instruction-selector-mips64.cc
diff --git a/src/compiler/mips64/instruction-selector-mips64.cc b/src/compiler/mips64/instruction-selector-mips64.cc
index d20c1c72f66a162b231b09f16bc07a78d9b6be50..8174846682bdba00466a4d29c1fdeab13104a1f2 100644
--- a/src/compiler/mips64/instruction-selector-mips64.cc
+++ b/src/compiler/mips64/instruction-selector-mips64.cc
@@ -321,6 +321,9 @@ void InstructionSelector::VisitWord32Clz(Node* node) {
 }
 
 
+void InstructionSelector::VisitWord32Ctz(Node* node) { UNREACHABLE(); }
+
+
 void InstructionSelector::VisitWord64Ror(Node* node) {
   VisitRRO(this, kMips64Dror, node);
 }