Remove LiveIntervals::trackingRegUnits().

With regunit liveness permanently enabled, this function would always
return true.

Also remove now obsolete code for checking physreg interference.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159006 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 2aea1e1..1a50210 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -1188,7 +1188,7 @@
 
       // Collect ranges for register units. These live ranges are computed on
       // demand, so just skip any that haven't been computed yet.
-      if (TargetRegisterInfo::isPhysicalRegister(Reg) && LIS.trackingRegUnits())
+      if (TargetRegisterInfo::isPhysicalRegister(Reg))
         for (MCRegUnitIterator Units(Reg, &TRI); Units.isValid(); ++Units)
           if (LiveInterval *LI = LIS.getCachedRegUnit(*Units))
             collectRanges(MO, LI, Entering, Internal, Exiting, OldIdx);