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

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, 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 code_generator;
 
 import 'glue.dart';
 
 import '../../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../../js/js.dart' as js;
@@ skipping 337 matching lines @@
 
   @override
   js.Expression visitThis(tree_ir.This node) {
     return new js.This();
   }
 
   @override
   js.Expression visitTypeOperator(tree_ir.TypeOperator node) {
     js.Expression value = visitExpression(node.value);
     List<js.Expression> typeArguments = visitExpressionList(node.typeArguments);
-    if (!node.isTypeTest) {
-      giveup(node, 'type casts not implemented.');
-    }
     DartType type = node.type;
-    // Note that the trivial (but special) cases of Object, dynamic, and Null
-    // are handled at build-time and must not occur in a TypeOperator.
-    assert(!type.isObject && !type.isDynamic);
     if (type is InterfaceType) {
       glue.registerIsCheck(type, registry);
       ClassElement clazz = type.element;
 
-      // We use the helper:
+      // We use one of the two helpers:
       //
       //     checkSubtype(value, $isT, typeArgs, $asT)
+      //     subtypeCast(value, $isT, typeArgs, $asT)
       //
       // Any of the last two arguments may be null if there are no type
       // arguments, and/or if no substitution is required.
+      Element function = node.isTypeTest
+          ? glue.getCheckSubtype()
+          : glue.getSubtypeCast();
 
       js.Expression isT = js.string(glue.getTypeTestTag(type));
 
       js.Expression typeArgumentArray = typeArguments.isNotEmpty
           ? new js.ArrayInitializer(typeArguments)
           : new js.LiteralNull();
 
       js.Expression asT = glue.hasStrictSubtype(clazz)
           ? js.string(glue.getTypeSubstitutionTag(clazz))
           : new js.LiteralNull();
 
       return buildStaticHelperInvocation(
-          glue.getCheckSubtype(),
+          function,
           <js.Expression>[value, isT, typeArgumentArray, asT]);
     } else if (type is TypeVariableType) {
       glue.registerIsCheck(type, registry);
+
+      Element function = node.isTypeTest
+          ? glue.getCheckSubtypeOfRuntimeType()
+          : glue.getSubtypeOfRuntimeTypeCast();
+
       // The only type argument is the type held in the type variable.
       js.Expression typeValue = typeArguments.single;
+
       return buildStaticHelperInvocation(
-          glue.getCheckSubtypeOfRuntime(),
+          function,
           <js.Expression>[value, typeValue]);
     }
     return giveup(node, 'type check unimplemented for $type.');
   }
 
   @override
   js.Expression visitVariableUse(tree_ir.VariableUse node) {
     return buildVariableAccess(node.variable);
   }
 
@@ skipping 135 matching lines @@
   void visitThrow(tree_ir.Throw node) {
     accumulator.add(new js.Throw(visitExpression(node.value)));
   }
 
   @override
   void visitRethrow(tree_ir.Rethrow node) {
     glue.reportInternalError('rethrow seen in JavaScript output');
   }
 
   @override
+  void visitUnreachable(tree_ir.Unreachable node) {
+    // Output nothing.
+    // TODO(asgerf): Emit a throw/return to assist local analysis in the VM?
+  }
+
+  @override
   void visitTry(tree_ir.Try node) {
     js.Block tryBlock = buildBodyBlock(node.tryBody);
     tree_ir.Variable exceptionVariable = node.catchParameters.first;
     js.VariableDeclaration exceptionParameter =
         new js.VariableDeclaration(getVariableName(exceptionVariable));
     js.Block catchBlock = buildBodyBlock(node.catchBody);
     js.Catch catchPart = new js.Catch(exceptionParameter, catchBlock);
     accumulator.add(new js.Try(tryBlock, catchPart, null));
   }
 
@@ skipping 124 matching lines @@
     List<js.Expression> arguments = visitExpressionList(node.arguments);
     return glue.generateTypeRepresentation(node.dartType, arguments);
   }
 
   visitFunctionExpression(tree_ir.FunctionExpression node) {
     // FunctionExpressions are currently unused.
     // We might need them if we want to emit raw JS nested functions.
     throw 'FunctionExpressions should not be used';
   }
 }