When generating IC stubs to test whether objects have a type that has seen before, the type of singleton objects is explicitly instantiated with a getType(cx) call. Instead, an identity comparison on the input object can be used. Doing the identity comparison is preferable because (a) it requires one less load, and more importantly (b) instantiating singleton types can bloat memory usage unnecessarily. Many objects with lazy singleton types will flow around the program without any need to ever instantiate the type.

Comment on attachment 710418 [details] [diff] [review] patch Review of attachment 710418 [details] [diff] [review]: ----------------------------------------------------------------- Good find.