Also compute MBB live-in lists in the new rewriter pass.

This deduplicates some code from the optimizing register allocators, and
it means that it is now possible to change the register allocators'
solutions simply by editing the VirtRegMap between the register
allocator pass and the rewriter.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158249 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed