[turbofan] Handle impossible types (Type::None()) in the backend.

src/compiler/instruction.h

 // Copyright 2014 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_INSTRUCTION_H_
 #define V8_COMPILER_INSTRUCTION_H_
 
 #include <deque>
 #include <iosfwd>
 #include <map>
@@ skipping 1131 matching lines @@
                      OutputFrameStateCombine::Ignore()) const;
   size_t GetTotalSize() const;
   size_t GetFrameCount() const;
   size_t GetJSFrameCount() const;
 
   MachineType GetType(size_t index) const {
     return values_.GetOperandType(index);
   }
   StateValueDescriptor* GetStateValueDescriptor() { return &values_; }
 
+  static const int kImpossibleValue = 0xdead;
+
  private:
   FrameStateType type_;
   BailoutId bailout_id_;
   OutputFrameStateCombine frame_state_combine_;
   size_t parameters_count_;
   size_t locals_count_;
   size_t stack_count_;
   StateValueDescriptor values_;
   MaybeHandle<SharedFunctionInfo> const shared_info_;
   FrameStateDescriptor* outer_state_;
@@ skipping 328 matching lines @@
 
 
 std::ostream& operator<<(std::ostream& os,
                          const PrintableInstructionSequence& code);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_H_