Treat Mul just like Add and Subtract

Treat Mul just like Add and Subtract

Like adds and subtracts, muls ripple only to the left so we can use
the same logic.

While we're here, add a print method to DemandedBits so it can be used
with -analyze, which we'll use in the testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249686 91177308-0d34-0410-b5e6-96231b3b80d8