CTZ instruction implemented as optional operator.

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

Index: src/compiler/mips/instruction-selector-mips.cc
diff --git a/src/compiler/mips/instruction-selector-mips.cc b/src/compiler/mips/instruction-selector-mips.cc
index 3c4b378553e69a9e66060fcff69dfaafb2971062..c69103a0a26d96e80d3bb802d9a42ba3d99ca76f 100644
--- a/src/compiler/mips/instruction-selector-mips.cc
+++ b/src/compiler/mips/instruction-selector-mips.cc
@@ -270,6 +270,9 @@ void InstructionSelector::VisitWord32Clz(Node* node) {
 }
 
 
+void InstructionSelector::VisitWord32Ctz(Node* node) { UNREACHABLE(); }
+
+
 void InstructionSelector::VisitInt32Add(Node* node) {
   MipsOperandGenerator g(this);