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
diff --git a/llvm/lib/CodeGen/LiveRangeEdit.cpp b/llvm/lib/CodeGen/LiveRangeEdit.cpp
index 765a39a..47da205 100644
--- a/llvm/lib/CodeGen/LiveRangeEdit.cpp
+++ b/llvm/lib/CodeGen/LiveRangeEdit.cpp
@@ -292,6 +292,7 @@
             if (VNInfo *SVNI = S.getVNInfoAt(Idx))
               S.removeValNo(SVNI);
           }
+          LI.removeEmptySubRanges();
         }
       }
     }