[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 432 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::TypeSigma(const Operator* sigma_op, Type* input) {
+  return Type::Intersect(input, SigmaTypeOf(sigma_op), zone());
+}
+
 Type* OperationTyper::TypeJSAdd(Type* lhs, Type* rhs) {
   lhs = ToPrimitive(lhs);
   rhs = ToPrimitive(rhs);
 
   if (!lhs->IsInhabited() || !rhs->IsInhabited()) {
     return Type::None();
   }
 
   if (lhs->Maybe(Type::String()) || rhs->Maybe(Type::String())) {
     if (lhs->Is(Type::String()) || rhs->Is(Type::String())) {
       return Type::String();
     } else {
       return Type::NumberOrString();
     }
   }
   lhs = ToNumber(lhs);
   rhs = ToNumber(rhs);
   return NumberAdd(lhs, rhs);
 }
 
 Type* OperationTyper::TypeJSSubtract(Type* lhs, Type* rhs) {
   return NumberSubtract(ToNumber(lhs), ToNumber(rhs));
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8