libiberty: add helper to swap doubly-linked list wrappers

This patch introduces a new helper to swap the contents of two
doubly-linked list wrappers. The new *_swap_lists operation exchanges
the first, last, and size fields, allowing two lists to be swapped
efficiently without iterating over their elements.

This helper is intended for cases where the ownership of a list must be
exchanged but swapping wrapper pointers is not possible. For simple
references to lists, when wrappers are dynamically allocated, swapping
the wrapper pointers themselves is sufficient and remains the preferred
approach.

This change adds the necessary declaration and definition macros to
doubly-linked-list.h and integrates them into the set of mutative
list operations.

The testsuite is updated accordingly to cover the new functionality.

include/ChangeLog:

	* doubly-linked-list.h
	(LINKED_LIST_SWAP_LISTS): Add new helper.
	(LINKED_LIST_DECL_SWAP_LISTS): Likewise.
	(LINKED_LIST_DEFN_SWAP_LISTS): Likewise.
	(LWRAPPERTYPE##_swap_lists): Likewise.

libiberty/ChangeLog:

	* testsuite/test-doubly-linked-list.c: Update.

include/doubly-linked-list.h

@@ -229,14 +229,13 @@ LTYPE##_remove (LWRAPPERTYPE *wrapper, LTYPE *node)			\
   return previous;							\
 }
 
-/* Generic swap.  */
+/* Swap two nodes in a list.  */
 #define LINKED_LIST_SWAP(LTYPE)			LTYPE##_swap
 
 #define LINKED_LIST_DECL_SWAP(LWRAPPERTYPE, LTYPE, EXPORT)		\
   EXPORT void								\
   LTYPE##_swap (LWRAPPERTYPE *wrapper, LTYPE *node1, LTYPE *node2)
 
-/* Swap two nodes in a list.  */
 #define LINKED_LIST_DEFN_SWAP(LWRAPPERTYPE, LTYPE, EXPORT)		\
 EXPORT void								\
 LTYPE##_swap (LWRAPPERTYPE *wrapper, LTYPE *node1, LTYPE *node2)	\
@@ -276,6 +275,34 @@ LTYPE##_swap (LWRAPPERTYPE *wrapper, LTYPE *node1, LTYPE *node2)	\
   }									\
 }
 
+/* Swap two lists, i.e. swap two wrappers.  */
+#define LINKED_LIST_SWAP_LISTS(LWRAPPERTYPE)	LWRAPPERTYPE##_swap_lists
+
+#define LINKED_LIST_DECL_SWAP_LISTS(LWRAPPERTYPE, LTYPE, EXPORT)	\
+  EXPORT void								\
+  LWRAPPERTYPE##_swap_lists (LWRAPPERTYPE *left_w, LWRAPPERTYPE *right_w)
+
+#define LINKED_LIST_DEFN_SWAP_LISTS(LWRAPPERTYPE, LTYPE, EXPORT)	\
+EXPORT void								\
+LWRAPPERTYPE##_swap_lists (LWRAPPERTYPE *left_w, LWRAPPERTYPE *right_w)	\
+{									\
+  {									\
+    LTYPE *temp = left_w->first;					\
+    left_w->first = right_w->first;					\
+    right_w->first = temp;						\
+  }									\
+  {									\
+    LTYPE *temp = left_w->last;						\
+    left_w->last = right_w->last;					\
+    right_w->last = temp;						\
+  }									\
+  {									\
+    unsigned int temp = left_w->size;					\
+    left_w->size = right_w->size;					\
+    right_w->size = temp;						\
+  }									\
+}
+
 /* Note: all the mutative operations below also update the data in the wrapper,
    i.e. first, last and size.  */
 #define LINKED_LIST_MUTATIVE_OPS_PROTOTYPE(LWRAPPERTYPE, LTYPE, EXPORT)	\
@@ -285,7 +312,8 @@ LTYPE##_swap (LWRAPPERTYPE *wrapper, LTYPE *node1, LTYPE *node2)	\
   LINKED_LIST_DECL_POP_FRONT(LWRAPPERTYPE, LTYPE, EXPORT);		\
   LINKED_LIST_DECL_POP_BACK(LWRAPPERTYPE, LTYPE, EXPORT);		\
   LINKED_LIST_DECL_REMOVE(LWRAPPERTYPE, LTYPE, EXPORT);			\
-  LINKED_LIST_DECL_SWAP(LWRAPPERTYPE, LTYPE, EXPORT)
+  LINKED_LIST_DECL_SWAP(LWRAPPERTYPE, LTYPE, EXPORT);			\
+  LINKED_LIST_DECL_SWAP_LISTS(LWRAPPERTYPE, LTYPE, EXPORT)
 
 #define LINKED_LIST_MUTATIVE_OPS_DECL(LWRAPPERTYPE, LTYPE, EXPORT)	\
   LINKED_LIST_DEFN_APPEND(LWRAPPERTYPE, LTYPE, EXPORT)			\
@@ -294,7 +322,8 @@ LTYPE##_swap (LWRAPPERTYPE *wrapper, LTYPE *node1, LTYPE *node2)	\
   LINKED_LIST_DEFN_POP_FRONT(LWRAPPERTYPE, LTYPE, EXPORT)		\
   LINKED_LIST_DEFN_POP_BACK(LWRAPPERTYPE, LTYPE, EXPORT)		\
   LINKED_LIST_DEFN_REMOVE(LWRAPPERTYPE, LTYPE, EXPORT)			\
-  LINKED_LIST_DEFN_SWAP(LWRAPPERTYPE, LTYPE, EXPORT)
+  LINKED_LIST_DEFN_SWAP(LWRAPPERTYPE, LTYPE, EXPORT);			\
+  LINKED_LIST_DEFN_SWAP_LISTS(LWRAPPERTYPE, LTYPE, EXPORT)
 
 
 /* Sorting.  */

libiberty/testsuite/test-doubly-linked-list.c

@@ -190,6 +190,8 @@ const int EXPECT_7 [] = { 10, 9, 2, 4, 3, 8, 11 };
 const int EXPECT_8 [] = { 2, 3, 4, 8, 9, 10, 11 };
 const int EXPECT_9 [] = { 3, 4, 8, 9, 10, 11 };
 const int EXPECT_10 [] = { 3, 4, 8, 9, 10 };
+const int EXPECT_11 [] = { 20, 21, 22 };
+const int EXPECT_12 [] = { 3, 4, 8, 9, 10 };
 const struct test_data_t test_data[] = {
   { .content = EXPECT_0, .size = sizeof(EXPECT_0) / sizeof(EXPECT_0[0]) },
   { .content = EXPECT_1, .size = sizeof(EXPECT_1) / sizeof(EXPECT_1[0]) },
@@ -202,6 +204,8 @@ const struct test_data_t test_data[] = {
   { .content = EXPECT_8, .size = sizeof(EXPECT_8) / sizeof(EXPECT_8[0]) },
   { .content = EXPECT_9, .size = sizeof(EXPECT_9) / sizeof(EXPECT_9[0]) },
   { .content = EXPECT_10, .size = sizeof(EXPECT_10) / sizeof(EXPECT_10[0]) },
+  { .content = EXPECT_11, .size = sizeof(EXPECT_11) / sizeof(EXPECT_11[0]) },
+  { .content = EXPECT_12, .size = sizeof(EXPECT_12) / sizeof(EXPECT_12[0]) },
 };
 
 int main (void)
@@ -272,5 +276,23 @@ int main (void)
   LINKED_LIST_POP_BACK(ListNodeType) (&wrapper);
   failures += ! check ("pop_back", &test_data[10], &wrapper);
 
+  LinkedListWrapperType other_wrapper = {
+    .first = NULL,
+    .last = NULL,
+    .size = 0,
+  };
+
+  LINKED_LIST_APPEND(ListNodeType) (&other_wrapper, l_new_node (20));
+  LINKED_LIST_APPEND(ListNodeType) (&other_wrapper, l_new_node (21));
+  LINKED_LIST_APPEND(ListNodeType) (&other_wrapper, l_new_node (22));
+
+  /* Swap wrappers once.  */
+  LINKED_LIST_SWAP_LISTS (LinkedListWrapperType) (&wrapper, &other_wrapper);
+  failures += ! check ("swap wrappers once", &test_data[11], &wrapper);
+
+  /* Swap wrappers twice.  */
+  LINKED_LIST_SWAP_LISTS (LinkedListWrapperType) (&wrapper, &other_wrapper);
+  failures += ! check ("swap wrappers twice", &test_data[12], &wrapper);
+
   exit (failures ? EXIT_FAILURE : EXIT_SUCCESS);
 }