Add a bisection step on the list of instructions before doing the linear

Add a bisection step on the list of instructions before doing the linear
simplification. It's not clear to me whether this can replace the first of the
linear instruction simplification stages or not, so I left it in.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72377 91177308-0d34-0410-b5e6-96231b3b80d8