Fix regression on side effects of tdiv.

tests/compiler/dart2js/side_effect_tdiv_regression_test.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.
+
+import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
+
+import 'compiler_helper.dart';
+import 'parser_helper.dart';
+
+const String TEST = r'''
+class A {
+  var field = 42;
+}
+main() {
+  var a = new A();
+  var b = [42, -1];
+  // Force a setter on [field].
+  if (false) a.field = 12;
+  var c = a.field;
+  print(b[0] ~/ b[1]);
+  return c + a.field;
+}
+''';
+
+void main() {
+  asyncTest(() => compileAll(TEST).then((generated) {
+    Expect.isTrue(generated.contains('return c + c;'));

[sra1, 2013/12/11 09:45:24]

How does adding the side effect in the mock library cause this to be correct?

[ngeoffray, 2013/12/16 13:31:41]

In order to get a.field GVN'ed, we need to see that ~/ does not have side
effects. If the mock library version does not have side effects, then the code
to fix the regression would not be necessary.

+  }));  
+}