Bug 1001222 - Implicitly use operands to JSOP_POS. (r=jandem)

js/src/jit-test/tests/ion/bug1001222.js

@@ -0,0 +1,5 @@
+function f(x, y) {
+  return +(x ? x : y), y >>> 0
+}
+f(0, -0)
+f(0, 2147483649)

js/src/jit/IonBuilder.cpp

@@ -3884,7 +3884,10 @@ bool
 IonBuilder::jsop_pos()
 {
     if (IsNumberType(current->peek(-1)->type())) {
-        // Already int32 or double.
+        // Already int32 or double. Set the operand as implicitly used so it
+        // doesn't get optimized out if it has no other uses, as we could bail
+        // out.
+        current->peek(-1)->setImplicitlyUsedUnchecked();
         return true;
     }