LiveIntervalAnalysis: Factor out code to update liveness on physreg def removal

This cleans up code and is more in line with the general philosophy of
modifying LiveIntervals through LiveIntervalAnalysis instead of changing
them directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226687 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveIntervalAnalysis.h

@@ -393,6 +393,8 @@ namespace llvm {
       return RegUnitRanges[Unit];
     }
 
+    void removePhysRegDefAt(unsigned Reg, SlotIndex Pos);
+
   private:
     /// Compute live intervals for all virtual registers.
     void computeVirtRegs();