Fix issue 10321 by invalidating previous "generate at use site" optimizations based on a pure instr…

tests/language/issue10321_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";
+
+// Regression test for dart2js that used to miscompile [A.foo].
+
+var global = 54;
+
+class A {
+  int a = 0;
+  int b = 42;
+  final int c = global;
+  foo() {
+    int start = a - 1;
+    a = 54;
+    if (b == 42) {
+      b = 32;
+    } else {
+      b = 42;
+    }
+    Expect.equals(-1, start);
+  }
+
+  bar() {
+    int start = a - c - 1;
+    a = 42;
+    if (b == 42) {
+      b = 32;
+    } else {
+      b = 42;
+    }
+    Expect.equals(-55, start);
+  }
+}
+
+main() {
+  new A().foo();
+  new A().bar();
+}