dart2js cps: Bugfix in assignment propagation into branch conditions.

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.
 
 library tree_ir.optimization.statement_rewriter;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 
 /**
@@ skipping 566 matching lines @@
     // Do not propagate assignments into the successor statements, since they
     // may be overwritten by assignments in the body.
     inEmptyEnvironment(() {
       node.next = visitStatement(node.next);
     });
 
     return node;
   }
 
   Statement visitIf(If node) {
-    node.condition = visitExpression(node.condition);
-
-    // Do not propagate assignments into branches.  Doing so will lead to code
-    // duplication.
-    // TODO(kmillikin): Rethink this. Propagating some assignments
-    // (e.g. variables) is benign.  If they can occur here, they should
-    // be handled well.

[asgerf, 2015/07/09 11:19:01]

This comment was just outdated. It's not really related to the change.

+    // Do not propagate assignments into branches.
     inEmptyEnvironment(() {
       node.thenStatement = visitStatement(node.thenStatement);
       node.elseStatement = visitStatement(node.elseStatement);
+    });
 
+    node.condition = visitExpression(node.condition);
+
+    inEmptyEnvironment(() {
       tryCollapseIf(node);
     });
 
     Statement reduced = combineStatementsInBranches(
         node.thenStatement,
         node.elseStatement,
         node.condition);
     if (reduced != null) {
       return reduced;
     }
@@ skipping 554 matching lines @@
   VariableUseVisitor(this.callback);
 
   visitVariableUse(VariableUse use) => callback(use);
 
   visitInnerFunction(FunctionDefinition node) {}
 
   static void visit(Expression node, VariableUseCallback callback) {
     new VariableUseVisitor(callback).visitExpression(node);
   }
 }