I proposed an optimization for "x << 0" (as part of a larger patch to optimize 2 ** x) but the issue was rejected:
http://bugs.python.org/issue21420#msg217802

Mark Dickson wrote (msg217863):
"There are many, many tiny optimisations we *could* be making in Objects/longobject.c; each of those potential optimisations adds to the cost of maintaining the code, detracts from readability, and potentially even slows down the common cases fractionally.  In general, I think we should only be applying this sort of optimization when there's a clear benefit to real-world code.  I don't think this one crosses that line."