* Dramatically rework liveness evaluation.

* Implement the first step of the Globals graph: Deleting nodes from function
  graphs.  In practice, these nodes need to be moved to the globals graph, but
  this will be taken care of later.  Note that the graphs computed right now are
  not strictly correct!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4681 91177308-0d34-0410-b5e6-96231b3b80d8