diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testInt32ToId.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testInt32ToId.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,35 @@
+function testInt32ToId()
+{
+  // Ensure that a property which is a negative integer that does not fit in a
+  // jsval is properly detected by the 'in' operator.
+  var obj = { "-1073741828": 17 };
+  var index = -1073741819;
+  var a = [];
+  for (var i = 0; i < 10; i++)
+  {
+    a.push(index in obj);
+    index--;
+  }
+
+  // Ensure that a property which is a negative integer that does not fit in a
+  // jsval is properly *not* detected by the 'in' operator.  In this case
+  // wrongly applying INT_TO_JSID to -2147483648 will shift off the sign bit
+  // (the only bit set in that number) and bitwise-or that value with 1,
+  // producing jsid(1) -- which actually represents "0", not "-2147483648".
+  // Thus 'in' will report a "-2147483648" property when none exists, because
+  // it thinks the request was really whether the object had property "0".
+  var obj2 = { 0: 17 };
+  var b = [];
+  var index = -(1 << 28);
+  for (var i = 0; i < 10; i++)
+  {
+    b.push(index in obj2);
+    index = index - (1 << 28);
+  }
+
+  return a.join(",") + b.join(",");
+}
+
+assertEq(testInt32ToId(),   
+	 "false,false,false,false,false,false,false,false,false,true" +
+	 "false,false,false,false,false,false,false,false,false,false");