Introduce register dump helper

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222379 91177308-0d34-0410-b5e6-96231b3b80d8
MachineVerifier: Report register for bad liveranges

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222380 91177308-0d34-0410-b5e6-96231b3b80d8
Add a print and verify pass after the RegisterCoalescer

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222381 91177308-0d34-0410-b5e6-96231b3b80d8
RegisterCoalescer: Improve debug messages

- Show "Considering..." message after flipping so you actually see the final
  destination vreg as destination.
- Add a message on final join, so you can grep for "Success" messages to obtain
  a list of which register got merged with which.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222382 91177308-0d34-0410-b5e6-96231b3b80d8