IfConverted should unuse inputs of the join it removes.

tests/language/issue11087_vm_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.
 
-// Make sure the engine does not infer the wrong type for [:A.foo:].
-
-import "package:expect/expect.dart";
+// Regression test for VM's IfConverted pass not keeping graph structure and
+// use lists in sync.
 
 class A {
-  foo() => this;
+  int x;
 }
 
-class B extends A {
+f() {
+  var a = new A();
+  a.x = (true ? 2 : 4);
+  return a.x;
 }
 
 main() {
-  Expect.isTrue(new B().foo() is B);
+  for (var i = 0; i < 10000; i++) f();
 }
+