dart2js cps: Clean up and avoid processing unreachable code.

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

 // Copyright (c) 2015, 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.
 
 library dart2js.cps_ir.gvn;
 
 import 'cps_ir_nodes.dart';
 import '../universe/side_effects.dart';
 import '../elements/elements.dart';
 import 'optimizers.dart' show Pass;
@@ skipping 578 matching lines @@
   }
 
   /// The `process` methods below do not insert the referenced arguments into
   /// the vector, but instead rely on them being inserted here.
   processReference(Reference ref) {
     if (vector == null) return;
     Primitive prim = ref.definition.effectiveDefinition;
     vector.add(gvnFor[prim] ?? prim);
   }
 
-  visitTypeTest(TypeTest node) {
+  processTypeTest(TypeTest node) {
     vector = [GvnCode.TYPE_TEST, node.dartType];
-    processReference(node.value);
-    node.typeArguments.forEach(processReference);
-    // Suppress processing of the interceptor argument.
   }
 
   processTypeTestViaFlag(TypeTestViaFlag node) {
     vector = [GvnCode.TYPE_TEST_VIA_FLAG, node.dartType];
   }
 
   processApplyBuiltinOperator(ApplyBuiltinOperator node) {
     vector = [GvnCode.BUILTIN_OPERATOR, node.operator.index];
   }
 
@@ skipping 86 matching lines @@
 
   @override
   processReference(Reference ref) {
     callback(ref);
   }
 
   static void forEach(Primitive node, ReferenceCallback callback) {
     new InputVisitor(callback).visit(node);
   }
 }