Assignment expressions in tree IR.

pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.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 js_tree_ir_builder;
 
 import '../../tree_ir/tree_ir_builder.dart' show Builder;
 import 'glue.dart' show Glue;
 import '../../dart2jslib.dart' show Selector, InternalErrorFunction;
 import '../../elements/elements.dart';
@@ skipping 38 matching lines @@
         getInterceptor,
         selector,
         <Expression>[getVariableUse(node.input)]);
   }
 
   Expression visitGetField(cps_ir.GetField node) {
     return new GetField(getVariableUse(node.object), node.field);
   }
 
   Statement visitSetField(cps_ir.SetField node) {
-    return new SetField(getVariableUse(node.object),
-                        node.field,
-                        getVariableUse(node.value),
-                        visit(node.body));
+    SetField setField =
+        new SetField(getVariableUse(node.object),
+                     node.field,
+                     getVariableUse(node.value));
+    return new ExpressionStatement(setField, visit(node.body));
   }
 
   Expression visitCreateBox(cps_ir.CreateBox node) {
     return new CreateBox();
   }
 
   Expression visitCreateInstance(cps_ir.CreateInstance node) {
     return new CreateInstance(
         node.classElement,
         node.arguments.map(getVariableUse).toList(growable: false),
         node.typeInformation.map(getVariableUse).toList(growable: false));
   }
 }