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

src/compiler/machine-operator.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_MACHINE_OPERATOR_H_
 #define V8_COMPILER_MACHINE_OPERATOR_H_
 
 #include "src/base/flags.h"
 #include "src/machine-type.h"
 
@@ skipping 278 matching lines @@
   const Operator* TruncateFloat32ToUint32();
   const Operator* TryTruncateFloat32ToInt64();
   const Operator* TryTruncateFloat64ToInt64();
   const Operator* TryTruncateFloat32ToUint64();
   const Operator* TryTruncateFloat64ToUint64();
   const Operator* ChangeInt32ToFloat64();
   const Operator* ChangeInt32ToInt64();
   const Operator* ChangeUint32ToFloat64();
   const Operator* ChangeUint32ToUint64();
 
+  // These are changes from impossible values (for example a smi-checked
+  // string).  They can safely emit an abort instruction, which should
+  // never be reached.
+  const Operator* ImpossibleToWord32();
+  const Operator* ImpossibleToWord64();
+  const Operator* ImpossibleToFloat32();
+  const Operator* ImpossibleToFloat64();
+  const Operator* ImpossibleToTagged();
+  const Operator* ImpossibleToBit();
+
   // These operators truncate or round numbers, both changing the representation
   // of the number and mapping multiple input values onto the same output value.
   const Operator* TruncateFloat64ToFloat32();
   const Operator* TruncateInt64ToInt32();
   const Operator* RoundFloat64ToInt32();
   const Operator* RoundInt32ToFloat32();
   const Operator* RoundInt64ToFloat32();
   const Operator* RoundInt64ToFloat64();
   const Operator* RoundUint32ToFloat32();
   const Operator* RoundUint64ToFloat32();
@@ skipping 368 matching lines @@
 };
 
 
 DEFINE_OPERATORS_FOR_FLAGS(MachineOperatorBuilder::Flags)
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_MACHINE_OPERATOR_H_