[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/common-operator.cc

Index: src/compiler/common-operator.cc
diff --git a/src/compiler/common-operator.cc b/src/compiler/common-operator.cc
index 571775aacee330fb32b9a24226c377696d918b87..aaed01fe5db25d7020eb078947ae873390a46753 100644
--- a/src/compiler/common-operator.cc
+++ b/src/compiler/common-operator.cc
@@ -191,6 +191,11 @@ RegionObservability RegionObservabilityOf(Operator const* op) {
   return OpParameter<RegionObservability>(op);
 }
 
+Type* TypeGuardTypeOf(Operator const* op) {
+  DCHECK_EQ(IrOpcode::kTypeGuard, op->opcode());
+  return OpParameter<Type*>(op);
+}
+
 std::ostream& operator<<(std::ostream& os,
                          const ZoneVector<MachineType>* types) {
   // Print all the MachineTypes, separated by commas.
@@ -798,6 +803,13 @@ const Operator* CommonOperatorBuilder::Phi(MachineRepresentation rep,
       rep);                                              // parameter
 }
 
+const Operator* CommonOperatorBuilder::TypeGuard(Type* type) {
+  return new (zone()) Operator1<Type*>(       // --
+      IrOpcode::kTypeGuard, Operator::kPure,  // opcode
+      "TypeGuard",                            // name
+      1, 0, 1, 1, 0, 0,                       // counts
+      type);                                  // parameter
+}
 
 const Operator* CommonOperatorBuilder::EffectPhi(int effect_input_count) {
   DCHECK(effect_input_count > 0);  // Disallow empty effect phis.