dart2js cps: Type casts and related changes to type propagation.

pkg/compiler/lib/src/cps_ir/cps_ir_builder.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.
 
 library dart2js.ir_builder;
 
 import '../compile_time_constants.dart' show BackendConstantEnvironment;
 import '../constants/constant_system.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart' show ConstantValue, PrimitiveConstantValue;
@@ skipping 2389 matching lines @@
     if (type.isMalformed) {
       FunctionElement helper = program.throwTypeErrorHelper;
       ErroneousElement element = type.element;
       ir.Primitive message = buildStringConstant(element.message);
       return buildStaticFunctionInvocation(
           helper,
           CallStructure.ONE_ARG,
           <ir.Primitive>[message]);
     }
 
+    List<ir.Primitive> typeArguments = const <ir.Primitive>[];
+    if (type is GenericType && type.typeArguments.isNotEmpty) {
+      typeArguments = type.typeArguments.map(buildTypeExpression).toList();
+    } else if (type is TypeVariableType) {
+      typeArguments = <ir.Primitive>[buildTypeVariableAccess(type)];
+    }
+
     if (isTypeTest) {
       // For type tests, we must treat specially the rare cases where `null`
       // satisfies the test (which otherwise never satisfies a type test).
       // This is not an optimization: the TypeOperator assumes that `null`
-      // cannot satisfy the type test.
+      // cannot satisfy the type test unless the type is a type variable.
       if (type.isObject || type.isDynamic) {
         // `x is Object` and `x is dynamic` are always true, even if x is null.
         return buildBooleanConstant(true);
       }
       if (type is InterfaceType && type.element == program.nullClass) {
         // `x is Null` is true if and only if x is null.
         return addPrimitive(new ir.Identical(value, buildNullConstant()));
       }
+      return addPrimitive(new ir.TypeTest(value, type, typeArguments));
+    } else {
+      return _continueWithExpression(
+              (k) => new ir.TypeCast(value, type, typeArguments, k));
     }
-    List<ir.Primitive> typeArguments = const <ir.Primitive>[];
-    if (type is GenericType && type.typeArguments.isNotEmpty) {
-      typeArguments = type.typeArguments.map(buildTypeExpression).toList();
-    } else if (type is TypeVariableType) {
-      typeArguments = <ir.Primitive>[buildTypeVariableAccess(type)];
-    }
-    ir.Primitive check = _continueWithExpression(
-            (k) => new ir.TypeOperator(value,
-                       type, typeArguments, k, isTypeTest: isTypeTest));
-    return check;
   }
 
   @override
   ir.Primitive buildIfNull(ir.Primitive value,
                            ir.Primitive buildRight(IrBuilder builder)) {
     ir.Primitive condition = _buildCheckNull(value);
     return buildConditional(condition, buildRight, (_) => value);
   }
 
   @override
@@ skipping 74 matching lines @@
   final DartType type;
   final LocalVariableElement exceptionVariable;
   final LocalVariableElement stackTraceVariable;
   final SubbuildFunction buildCatchBlock;
 
   CatchClauseInfo({this.type,
                    this.exceptionVariable,
                    this.stackTraceVariable,
                    this.buildCatchBlock});
 }