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

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 358 matching lines @@
   V(TruncateFloat32ToInt32)     \
   V(TruncateFloat32ToUint32)    \
   V(TryTruncateFloat32ToInt64)  \
   V(TryTruncateFloat64ToInt64)  \
   V(TryTruncateFloat32ToUint64) \
   V(TryTruncateFloat64ToUint64) \
   V(ChangeInt32ToFloat64)       \
   V(ChangeInt32ToInt64)         \
   V(ChangeUint32ToFloat64)      \
   V(ChangeUint32ToUint64)       \
+  V(ImpossibleToBit)            \

[Benedikt Meurer, 2016/07/24 17:23:41]

Hm, why not have a single Impossible machine/common operator, with a
MachineRepresentation parameter? That would also simplify the instruction
selection code.

[Jarin, 2016/07/24 18:15:40]

It just seemed that parametrized machine ops are discouraged. I think I prefer
this explicit way - it is nice when the output representation is obvious from
the opcode.

[Benedikt Meurer, 2016/07/25 03:36:51]

I'd have made this a common operator in the same spirit as Phi/Select that know
their representation. But acknowledge your decision.

+  V(ImpossibleToWord32)         \
+  V(ImpossibleToWord64)         \
+  V(ImpossibleToFloat32)        \
+  V(ImpossibleToFloat64)        \
+  V(ImpossibleToTagged)         \
   V(TruncateFloat64ToFloat32)   \
   V(TruncateInt64ToInt32)       \
   V(RoundFloat64ToInt32)        \
   V(RoundInt32ToFloat32)        \
   V(RoundInt64ToFloat32)        \
   V(RoundInt64ToFloat64)        \
   V(RoundUint32ToFloat32)       \
   V(RoundUint64ToFloat32)       \
   V(RoundUint64ToFloat64)       \
   V(BitcastFloat32ToInt32)      \
@@ skipping 333 matching lines @@
   }
 };
 
 std::ostream& operator<<(std::ostream&, IrOpcode::Value);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_OPCODES_H_