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

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index e9045d114499ef3e45b9dba8e439105ecfe4a688..f82229a630fbf2c29527ba3b58723a043e2c2bd5 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -296,6 +296,16 @@ class MachineOperatorBuilder final : public ZoneObject {
   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();