[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/opcodes.h

 // Copyright 2013 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_OPCODES_H_
 #define V8_COMPILER_OPCODES_H_
 
 #include <iosfwd>
 
 // Opcodes for control operators.
@@ skipping 43 matching lines @@
   V(FrameState)           \
   V(StateValues)          \
   V(TypedStateValues)     \
   V(ObjectState)          \
   V(Call)                 \
   V(Parameter)            \
   V(OsrValue)             \
   V(LoopExit)             \
   V(LoopExitValue)        \
   V(LoopExitEffect)       \
-  V(Projection)
+  V(Projection)           \
+  V(Sigma)
 
 #define COMMON_OP_LIST(V) \
   CONSTANT_OP_LIST(V)     \
   INNER_OP_LIST(V)        \
   V(Dead)
 
 // Opcodes for JavaScript operators.
 #define JS_COMPARE_BINOP_LIST(V) \
   V(JSEqual)                     \
   V(JSNotEqual)                  \
@@ skipping 664 matching lines @@
   }
 };
 
 std::ostream& operator<<(std::ostream&, IrOpcode::Value);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_OPCODES_H_