LiveRangeEdit: Check for completely empy subranges after removing ValNos.

Completely empty subranges are not allowed and must be removed when
subreg liveness is enabled.

llvm-svn: 224804

lib/CodeGen/LiveRangeEdit.cpp

@@ -292,6 +292,7 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
             if (VNInfo *SVNI = S.getVNInfoAt(Idx))
               S.removeValNo(SVNI);
           }
+          LI.removeEmptySubRanges();
         }
       }
     }