Fix an error in optimized modulus operator, add unit test.

test/mjsunit/div-mod.js

 // Copyright 2009 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
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@@ skipping 151 matching lines @@
   var zero = 0;
   var minsmi32 = -0x40000000;
   var minsmi64 = -0x80000000;
   var somenum = 3532;
   assertEquals(-0, zero / -1, "0 / -1");
   assertEquals(1, minsmi32 / -0x40000000, "minsmi/minsmi-32");
   assertEquals(1, minsmi64 / -0x80000000, "minsmi/minsmi-64");
   assertEquals(somenum, somenum % -0x40000000, "%minsmi-32");
   assertEquals(somenum, somenum % -0x80000000, "%minsmi-64");
 })();
+
+
+// Side-effect-free expressions containing bit operations use
+// an optimized compiler with int32 values.   Ensure that modulus
+// produces negative zeros correctly.
+function negative_zero_modulus_test() {
+  var x = 4;
+  var y = -4;
+  x = x + x - x;
+  y = y + y - y;
+  var z = (y | y | y | y) % x;
+  assertEquals(-1 / 0, 1 / z);
+  z = (x | x | x | x) % x;
+  assertEquals(1 / 0, 1 / z);
+  z = (y | y | y | y) % y;
+  assertEquals(-1 / 0, 1 / z);
+  z = (x | x | x | x) % y;
+  assertEquals(1 / 0, 1 / z);
+}
+
+negative_zero_modulus_test();