While SimplifyDemandedBits constant folds this, we can't rely on it here.

It's possible to craft an input that hits the recursion limits in a way
that SimplifyDemandedBits doesn't simplify the icmp but ComputeMaskedBits
can infer which bits are zero.

No test case as it depends on too many other things. Fixes PR9609.

llvm-svn: 128777