Now that I am told MachineRegisterInfo also tracks physical register uses / defs...

Now that I am told MachineRegisterInfo also tracks physical register uses / defs, I can do away with the horribleness I introduced a while back. It's impossible to detect if there is any use of a physical register below an instruction (and before any def of the register) with some cheap book keeping.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@49105 91177308-0d34-0410-b5e6-96231b3b80d8