diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testMissingProperties.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testMissingProperties.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,49 @@
+function isnan(n) { return n !== n }
+
+function f(x) {
+    var sum = 0;
+    for (var i = 0; i < 100; ++i)
+        sum += x.x;
+    return sum;
+}
+var o = {};
+assertEq(isnan(f(o)), true);
+o.x = 1;
+assertEq(f(o), 100);
+var o = {a:1, b:2};
+assertEq(isnan(f(o)), true);
+o.x = 2;
+assertEq(f(o), 200);
+
+function g(x) {
+    var sum = 0;
+    for (var i = 0; i < 100; ++i)
+        sum += x.x;
+    return sum;
+}
+var o = {c:1, x:1};
+assertEq(g(o), 100);
+var o = {};
+assertEq(isnan(g(o)), true);
+
+function h(x) {
+    var sum = 0;
+    for (var i = 0; i < 100; ++i)
+        sum += x.x;
+    return sum;
+}
+
+var proto1 = {};
+var proto2 = Object.create(proto1);
+var o = Object.create(proto2);
+assertEq(isnan(f(o)), true);
+assertEq(isnan(g(o)), true);
+assertEq(isnan(h(o)), true);
+proto2.x = 2;
+assertEq(f(o), 200);
+assertEq(g(o), 200);
+assertEq(h(o), 200);
+var o = {}
+assertEq(isnan(f(o)), true);
+assertEq(isnan(g(o)), true);
+assertEq(isnan(h(o)), true);