[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/operation-typer.cc

Index: src/compiler/operation-typer.cc
diff --git a/src/compiler/operation-typer.cc b/src/compiler/operation-typer.cc
index 7f6650af36219cd3a878dca95d04464a736d353d..e81c81b567fe806a4bafff58c9f5f6793a9cfd7c 100644
--- a/src/compiler/operation-typer.cc
+++ b/src/compiler/operation-typer.cc
@@ -4,6 +4,7 @@
 
 #include "src/compiler/operation-typer.h"
 
+#include "src/compiler/common-operator.h"
 #include "src/factory.h"
 #include "src/isolate.h"
 #include "src/type-cache.h"
@@ -911,6 +912,10 @@ Type* OperationTyper::FalsifyUndefined(ComparisonOutcome outcome) {
   return singleton_true();
 }
 
+Type* OperationTyper::TypeTypeGuard(const Operator* sigma_op, Type* input) {
+  return Type::Intersect(input, TypeGuardTypeOf(sigma_op), zone());
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8