Add an assertion for a likely ilist::splice() contract violation.
The single-element ilist::splice() function supports a noop move:
List.splice(I, List, I);
The corresponding std::list function doesn't allow that, so add a unit
test to document that behavior.
This also means that
List.splice(I, List, F);
is somewhat surprisingly not equivalent to
List.splice(I, List, F, next(F));
This patch adds an assertion to catch the illegal case I == F above.
Alternatively, we could make I == F a legal noop, but that would make
ilist differ even more from std::list.
llvm-svn: 170443