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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170443 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 0 deletions

diff --git a/include/llvm/ADT/ilist.h b/include/llvm/ADT/ilist.h
index 7f5cd17181..36650d4375 100644
--- a/include/llvm/ADT/ilist.h
+++ b/include/llvm/ADT/ilist.h
@@ -472,6 +472,10 @@ private:
   //
   void transfer(iterator position, iplist &L2, iterator first, iterator last) {
     assert(first != last && "Should be checked by callers");
+    // Position cannot be contained in the range to be transferred.
+    // Check for the most common mistake.
+    assert(position != first &&
+           "Insertion point can't be one of the transferred nodes");
 
     if (position != last) {
       // Note: we have to be careful about the case when we move the first node