Introduce Register Units: Give each leaf register a number.

First small step toward modeling multi-register multi-pressure. In the
future, register units can also be used to model liveness and
aliasing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153794 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed