gdb: use intrusive list for step-over chain

The threads that need a step-over are currently linked using an
hand-written intrusive doubly-linked list, so that seems a very good
candidate for intrusive_list, convert it.

For this, we have a use case of appending a list to another one (in
start_step_over).  Based on the std::list and Boost APIs, add a splice
method.  However, only support splicing the other list at the end of the
`this` list, since that's all we need.

Add explicit default assignment operators to
reference_to_pointer_iterator, which are otherwise implicitly deleted.
This is needed because to define thread_step_over_list_safe_iterator, we
wrap reference_to_pointer_iterator inside a basic_safe_iterator, and
basic_safe_iterator needs to be able to copy-assign the wrapped
iterator.  The move-assignment operator is therefore not needed, only
the copy-assignment operator is.  But for completeness, add both.

Change-Id: I31b2ff67c7b78251314646b31887ef1dfebe510c

1 files changed, 84 insertions, 0 deletions

diff --git a/gdb/unittests/intrusive_list-selftests.c b/gdb/unittests/intrusive_list-selftests.c
index 5497a012dd9..8b2b2d1391e 100644
--- a/gdb/unittests/intrusive_list-selftests.c
+++ b/gdb/unittests/intrusive_list-selftests.c
@@ -504,6 +504,89 @@ struct intrusive_list_test
   }
 
   static void
+  test_splice ()
+  {
+    {
+      /* Two non-empty lists.  */
+      item_type a ("a"), b ("b"), c ("c"), d ("d"), e ("e");
+      ListType list1;
+      ListType list2;
+      std::vector<const item_type *> expected;
+
+      list1.push_back (a);
+      list1.push_back (b);
+      list1.push_back (c);
+
+      list2.push_back (d);
+      list2.push_back (e);
+
+      list1.splice (std::move (list2));
+
+      expected = {&a, &b, &c, &d, &e};
+      verify_items (list1, expected);
+
+      expected = {};
+      verify_items (list2, expected);
+    }
+
+    {
+      /* Receiving list empty.  */
+      item_type a ("a"), b ("b"), c ("c");
+      ListType list1;
+      ListType list2;
+      std::vector<const item_type *> expected;
+
+      list2.push_back (a);
+      list2.push_back (b);
+      list2.push_back (c);
+
+      list1.splice (std::move (list2));
+
+      expected = {&a, &b, &c};
+      verify_items (list1, expected);
+
+      expected = {};
+      verify_items (list2, expected);
+    }
+
+    {
+      /* Giving list empty.  */
+      item_type a ("a"), b ("b"), c ("c");
+      ListType list1;
+      ListType list2;
+      std::vector<const item_type *> expected;
+
+      list1.push_back (a);
+      list1.push_back (b);
+      list1.push_back (c);
+
+      list1.splice (std::move (list2));
+
+      expected = {&a, &b, &c};
+      verify_items (list1, expected);
+
+      expected = {};
+      verify_items (list2, expected);
+    }
+
+    {
+      /* Both lists empty.  */
+      item_type a ("a"), b ("b"), c ("c");
+      ListType list1;
+      ListType list2;
+      std::vector<const item_type *> expected;
+
+      list1.splice (std::move (list2));
+
+      expected = {};
+      verify_items (list1, expected);
+
+      expected = {};
+      verify_items (list2, expected);
+    }
+  }
+
+  static void
   test_pop_front ()
   {
     item_type a ("a"), b ("b"), c ("c");
@@ -682,6 +765,7 @@ test_intrusive_list ()
   tests.test_push_front ();
   tests.test_push_back ();
   tests.test_insert ();
+  tests.test_splice ();
   tests.test_pop_front ();
   tests.test_pop_back ();
   tests.test_erase ();