dart2js cps: Always use interceptors and type tags for 'is' checks.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // IrNodes are kept in a separate library to have precise control over their
 // dependencies on other parts of the system.
 library dart2js.ir_nodes;
 
 import '../constants/expressions.dart';
 import '../constants/values.dart' as values show ConstantValue;
@@ skipping 23 matching lines @@
   // The head of a linked-list of occurrences, in no particular order.
   Reference<T> firstRef;
 
   bool get hasAtMostOneUse  => firstRef == null || firstRef.next == null;
   bool get hasExactlyOneUse => firstRef != null && firstRef.next == null;
   bool get hasNoUses => firstRef == null;
   bool get hasAtLeastOneUse => firstRef != null;
   bool get hasMultipleUses  => !hasAtMostOneUse;
 
   void substituteFor(Definition<T> other) {
+    if (other == this) return;
     if (other.hasNoUses) return;
     Reference<T> previous, current = other.firstRef;
     do {
       current.definition = this;
       previous = current;
       current = current.next;
     } while (current != null);
     previous.next = firstRef;
     if (firstRef != null) firstRef.previous = previous;
     firstRef = other.firstRef;
@@ skipping 340 matching lines @@
   }
 
   accept(Visitor visitor) => visitor.visitInvokeConstructor(this);
 }
 
 /// "as" casts and "is" checks.
 // We might want to turn "is"-checks into a [Primitive] as it can never diverge.
 // But then we need to special-case for is-checks with an erroneous .type as
 // these will throw.
 class TypeOperator extends Expression {
-  final Reference<Primitive> receiver;
+  Reference<Primitive> receiver;
   final DartType type;
   final Reference<Continuation> continuation;
   // TODO(johnniwinther): Use `Operator` class to encapsule the operator type.
   final bool isTypeTest;
 
   TypeOperator(Primitive receiver,
                this.type,
                Continuation cont,
                {bool this.isTypeTest})
       : this.receiver = new Reference<Primitive>(receiver),
@@ skipping 992 matching lines @@
     processNonTailThrow(node);
     processReference(node.value);
   }
 
   processCreateInvocationMirror(CreateInvocationMirror node) {}
   visitCreateInvocationMirror(CreateInvocationMirror node) {
     processCreateInvocationMirror(node);
     node.arguments.forEach(processReference);
   }
 }