diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testConcatNWithSideEffects.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testConcatNWithSideEffects.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,12 @@
+var log;
+function b(x) { log += 'b'; return 'B'; }
+function g() {
+    log = '';
+    var a = {toString: function () { log += 'a'; return 'A'; }};
+    assertEq("[" + a + b() + "]", "[AB]");
+    assertEq(log, "ab");
+}
+
+for (var i = 0; i < 1000; ++i)
+    g();
+