diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/ion/bug878510.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/ion/bug878510.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,20 @@
+function neg0(x) {
+  return x===0 && (1/x)===-Infinity;
+}
+
+function test(x,y) {
+  if (x == 1.1)
+    return 0;
+  else if (x == "a")
+    return 0;
+  return x*y
+}
+
+var t = 0;
+for(var i=0; i<1005; i++) {
+  test(1.1)
+  test("a")
+  t = test((i<1003)?i:-0, 0);
+}
+
+assertEq(neg0(t), true);