[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/operation-typer.h

Index: src/compiler/operation-typer.h
diff --git a/src/compiler/operation-typer.h b/src/compiler/operation-typer.h
index 0b039a928dd5a1cb9702aad3631629b8298ba5c4..bd271bdab3ff8210b6a880efd6f1aca9e02ed16d 100644
--- a/src/compiler/operation-typer.h
+++ b/src/compiler/operation-typer.h
@@ -19,6 +19,8 @@ class Zone;
 
 namespace compiler {
 
+class Operator;
+
 class OperationTyper {
  public:
   OperationTyper(Isolate* isolate, Zone* zone);
@@ -43,6 +45,8 @@ class OperationTyper {
   SIMPLIFIED_SPECULATIVE_NUMBER_BINOP_LIST(DECLARE_METHOD)
 #undef DECLARE_METHOD
 
+  Type* TypeTypeGuard(const Operator* sigma_op, Type* input);
+
   enum ComparisonOutcomeFlags {
     kComparisonTrue = 1,
     kComparisonFalse = 2,