* Minor cleanups

* Minor cleanups
* Eliminate the KillList instance variable, instead, just delete loads and
  stores as they are "renamed", and delete allocas when they are done
* Make the 'visited' set an instance variable to avoid passing it on the stack.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8857 91177308-0d34-0410-b5e6-96231b3b80d8