Fix some bugs that blocked optimizations in the new IRs.

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.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.
 
 part of tree_ir.optimization;
 
 /**
  * Performs the following transformations on the tree:
  * - Assignment propagation
  * - If-to-conditional conversion
@@ skipping 391 matching lines @@
     List<Assign> savedEnvironment = environment;
     environment = <Assign>[];
     node.next = visitStatement(node.next);
     assert(environment.isEmpty);
     environment = savedEnvironment;
     return node;
   }
 
   Statement visitSetField(SetField node) {
     node.next = visitStatement(node.next);
+    node.value = visitExpression(node.value);
     node.object = visitExpression(node.object);
-    node.value = visitExpression(node.value);
     return node;
   }
 
   Expression visitGetField(GetField node) {
     node.object = visitExpression(node.object);
     return node;
   }
 
   Expression visitCreateBox(CreateBox node) {
     return node;
@@ skipping 165 matching lines @@
   }
 
   Expression makeCondition(Expression e, bool polarity) {
     return polarity ? e : new Not(e);
   }
 
   Statement getBranch(If node, bool polarity) {
     return polarity ? node.thenStatement : node.elseStatement;
   }
 }