[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/operation-typer.h

 // 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.
 
 #ifndef V8_COMPILER_OPERATION_TYPER_H_
 #define V8_COMPILER_OPERATION_TYPER_H_
 
 #include "src/base/flags.h"
 #include "src/compiler/opcodes.h"
 
 namespace v8 {
 namespace internal {
 
 class Isolate;
 class RangeType;
 class Type;
 class TypeCache;
 class Zone;
 
 namespace compiler {
 
+class Operator;
+
 class OperationTyper {
  public:
   OperationTyper(Isolate* isolate, Zone* zone);
 
   // Typing Phi.
   Type* Merge(Type* left, Type* right);
 
   Type* ToPrimitive(Type* type);
 
   // Helpers for number operation typing.
   Type* ToNumber(Type* type);
   Type* WeakenRange(Type* current_range, Type* previous_range);
 
   Type* NumberAdd(Type* lhs, Type* rhs);
   Type* NumberSubtract(Type* lhs, Type* rhs);
   Type* NumberMultiply(Type* lhs, Type* rhs);
   Type* NumberDivide(Type* lhs, Type* rhs);
   Type* NumberModulus(Type* lhs, Type* rhs);
 
   Type* NumberAbs(Type* type);
 
+  Type* TypeSigma(const Operator* sigma_op, Type* input);
+
   enum ComparisonOutcomeFlags {
     kComparisonTrue = 1,
     kComparisonFalse = 2,
     kComparisonUndefined = 4
   };
 
 // Javascript binop typers.
 #define DECLARE_CASE(x) Type* Type##x(Type* lhs, Type* rhs);
   JS_SIMPLE_BINOP_LIST(DECLARE_CASE)
 #undef DECLARE_CASE
@@ skipping 24 matching lines @@
   Type* singleton_false_;
   Type* singleton_true_;
   Type* singleton_the_hole_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_OPERATION_TYPER_H_