Avoid creating invalid TypeMask.nonNullExact

pkg/compiler/lib/src/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;
 
 class SsaFunctionCompiler implements FunctionCompiler {
   final SsaCodeGeneratorTask generator;
   final SsaBuilderTask builder;
   final SsaOptimizerTask optimizer;
@@ skipping 5711 matching lines @@
                          {SourceInformation sourceInformation}) {
 
     // We prefer to not inline certain operations on indexables,
     // because the constant folder will handle them better and turn
     // them into simpler instructions that allow further
     // optimizations.
     bool isOptimizableOperationOnIndexable(Selector selector, Element element) {
       bool isLength = selector.isGetter
           && selector.name == "length";
       if (isLength || selector.isIndex) {
-        TypeMask type = new TypeMask.nonNullExact(
-            element.enclosingClass.declaration, compiler.world);
-        return type.satisfies(backend.jsIndexableClass, compiler.world);
+        return compiler.world.isSubtypeOf(
+            element.enclosingClass.declaration,
+            backend.jsIndexableClass);
       } else if (selector.isIndexSet) {
-        TypeMask type = new TypeMask.nonNullExact(
-            element.enclosingClass.declaration, compiler.world);
-        return type.satisfies(backend.jsMutableIndexableClass, compiler.world);
+        return compiler.world.isSubtypeOf(
+            element.enclosingClass.declaration,
+            backend.jsMutableIndexableClass);
       } else {
         return false;
       }
     }
 
     bool isOptimizableOperation(Selector selector, Element element) {
       ClassElement cls = element.enclosingClass;
       if (isOptimizableOperationOnIndexable(selector, element)) return true;
       if (!backend.interceptedClasses.contains(cls)) return false;
       if (selector.isOperator) return true;
@@ skipping 3246 matching lines @@
     if (unaliased is TypedefType) throw 'unable to unalias $type';
     unaliased.accept(this, builder);
   }
 
   void visitDynamicType(DynamicType type, SsaBuilder builder) {
     JavaScriptBackend backend = builder.compiler.backend;
     ClassElement cls = backend.findHelper('DynamicRuntimeType');
     builder.push(new HDynamicType(type, new TypeMask.exact(cls, classWorld)));
   }
 }