[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/operation-typer.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #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"
 #include "src/types.h"
 
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ skipping 887 matching lines @@
   if ((outcome & kComparisonFalse) != 0 ||
       (outcome & kComparisonUndefined) != 0) {
     return (outcome & kComparisonTrue) != 0 ? Type::Boolean()
                                             : singleton_false();
   }
   // Type should be non empty, so we know it should be true.
   DCHECK((outcome & kComparisonTrue) != 0);
   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