assuming const global references for @jit decorated classes and functions

[thautwarm]

F = ...

@jit
def f(x):
   return F(x)

In order to get extreme performance gain, flags can be set to break CPython semantics so that F always referenced to the object we've seen, instead of allowing later mutations.

[thautwarm]

It is observed that in usual cases, global references wouldn't change at all. If you want to use a mutable global variable in @jit functions, maybe writing globals()[name] is better?