diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/arrayConcat.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/arrayConcat.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,18 @@
+
+/* Test concat compiler paths. */
+
+for (var i = 9; i < 10; i++)
+  assertEq([2].concat([3])[0], 2);
+
+function f(a, b) {
+  return a.concat(b)[0];
+}
+function g() {
+  var x = [];
+  var y = [1];
+  for (var i = 0; i < 50; i++)
+    assertEq(f(x, y), 1);
+  eval('y[0] = "three"');
+  assertEq(f(x, y), "three");
+}
+g();