Fix bug in constant propagation with double-equality.

tests/language/arithmetic_test.dart

 // Copyright (c) 2012, 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.
 // Dart test program to test arithmetic operations.
 
 library arithmetic_test;
 import "package:expect/expect.dart";
 import 'dart:math';
 
 class ArithmeticTest {
@@ skipping 417 matching lines @@
   }
 
   static mySqrt(var x) => sqrt(x);
 
   static testSqrtDeopt() {
     for (var i = 0; i < 10; i++) mySqrt(4.0);
     Expect.equals(2.0, mySqrt(4.0));
     Expect.throws(() => mySqrt("abc"));
   }
 
+  static self_equality(x) {
+    return x == x;
+  }
+
+  static testDoubleEquality() {
+    Expect.isFalse(self_equality(double.NAN));
+    for (int i = 0; i < 2000; i++) {
+      self_equality(3.0);
+    }
+    Expect.isFalse(self_equality(double.NAN));
+  }
+
   static testMain() {
     for (int i = 0; i < 1500; i++) {
       runOne();
       testSmiDivDeopt();
       testSqrtDeopt();
+      testDoubleEquality();
     }
   }
 }
 
 main() {
   ArithmeticTest.testMain();
 }