These splices are interesting because they involve swapping two nodes in
the same list. There are two ways to do this. Assuming:
A -> B -> [Sentinel]
You can either:
- splice B before A, with: L.splice(A, L, B) or
- splice A before Sentinel, with: L.splice(L.end(), L, A) to create:
B -> A -> [Sentinel]
These two swapping-splices are somewhat interesting corner cases for
maintaining the list invariants. The tests pass even with my new ilist
implementation, but I had some doubts about the latter when I was
looking at weird UB effects. Since I can't find equivalent explicit
test coverage elsewhere it seems prudent to commit.
llvm-svn: 278887
4741661573