Use assertSubtype for lists.

sdk/lib/_internal/compiler/implementation/ssa/builder.dart

 // Copyright (c) 2012, 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.
 
 part of ssa;
 
 /**
  * A special element for the extra parameter taken by intercepted
  * methods. We need to override [Element.computeType] because our
  * optimizers may look at its declared type.
@@ skipping 2823 matching lines @@
   HInstruction buildIsNode(Node node, DartType type, HInstruction expression) {
     if (type.kind == TypeKind.TYPE_VARIABLE) {
       HInstruction runtimeType = addTypeVariableReference(type);
       Element helper = backend.getCheckSubtypeOfRuntimeType();
       List<HInstruction> inputs = <HInstruction>[expression, runtimeType];
       pushInvokeStatic(null, helper, inputs, HType.BOOLEAN);
       HInstruction call = pop();
       return new HIs(type, <HInstruction>[expression, call],
                      HIs.VARIABLE_CHECK);
     } else if (RuntimeTypes.hasTypeArguments(type)) {
-      Element element = type.element;
+      ClassElement element = type.element;
       Element helper = backend.getCheckSubtype();
       HInstruction representations =
           buildTypeArgumentRepresentations(type);
       add(representations);
       String operator =
           backend.namer.operatorIs(backend.getImplementationClass(element));
       HInstruction isFieldName = addConstantString(node, operator);
-      // TODO(karlklose): use [:null:] for [asField] if [element] does not
-      // have a subclass.
-      HInstruction asFieldName =
-          addConstantString(node, backend.namer.substitutionName(element));
+      HInstruction asFieldName = compiler.world.hasAnySubtype(element)
+          ? addConstantString(node, backend.namer.substitutionName(element))
+          : graph.addConstantNull(constantSystem);
       List<HInstruction> inputs = <HInstruction>[expression,
                                                  isFieldName,
                                                  representations,
                                                  asFieldName];
       pushInvokeStatic(node, helper, inputs, HType.BOOLEAN);
       HInstruction call = pop();
       return
           new HIs(type, <HInstruction>[expression, call], HIs.COMPOUND_CHECK);
     } else {
       return new HIs(type, <HInstruction>[expression], HIs.RAW_CHECK);
@@ skipping 2538 matching lines @@
           new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }