diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testArrayDensityChange.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testArrayDensityChange.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,17 @@
+function testArrayDensityChange() {
+  var x = [];
+  var count = 0;
+  for (var i=0; i < 100; ++i) {
+    x[i] = "asdf";
+  }
+  for (var i=0; i < x.length; ++i) {
+      if (i == 51)
+      {
+        x[199] = "asdf";
+      }
+      if (x[i])
+        count += x[i].length;
+  }
+  return count;
+}
+assertEq(testArrayDensityChange(), 404);