Add test case for r311511

This also changes the TailDuplicator to be configured explicitely
pre/post regalloc rather than relying on the isSSA() flag. This was
necessary to have `llc -run-pass` work reliably.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311520 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed