CTZ instruction implemented as optional operator.

src/compiler/x64/code-generator-x64.cc

Index: src/compiler/x64/code-generator-x64.cc
diff --git a/src/compiler/x64/code-generator-x64.cc b/src/compiler/x64/code-generator-x64.cc
index f14412b75785b40e709b94003ca35d77c7bd3792..1295b5ad40b6c1f8216c2ee5df9b49c72621b0bf 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -770,6 +770,13 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
         __ Lzcntl(i.OutputRegister(), i.InputOperand(0));
       }
       break;
+    case kX64Tzcnt32:
+      if (instr->InputAt(0)->IsRegister()) {
+        __ Tzcntl(i.OutputRegister(), i.InputRegister(0));
+      } else {
+        __ Tzcntl(i.OutputRegister(), i.InputOperand(0));
+      }
+      break;
     case kSSEFloat32Cmp:
       ASSEMBLE_SSE_BINOP(ucomiss);
       break;