rbtree: inline rb_last()

This is a very small function, inlining it saves cpu cycles in TCP by
reducing register pressure and removing call/ret overhead.

It also reduces vmlinux text size by 122 bytes on a typical x86_64 build.

Before:

size vmlinux
text data bss dec hex filename
34811781 22177365 5685248 62674394 3bc55da vmlinux

After:

size vmlinux
text data bss dec hex filename
34811659 22177365 5685248 62674272 3bc5560 vmlinux

[[e-mail]: fix rust build]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: Miguel Ojeda <[e-mail]>
Reviewed-by: Kuan-Wei Chiu <[e-mail]>
Cc: Jakub Kacinski <[e-mail]>
Cc: Neal Cardwell <[e-mail]>
Cc: Paolo Abeni <[e-mail]>
Cc: Alice Ryhl <[e-mail]>
Cc: Stehen Rothwell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/rbtree.h

···
 		n = n->rb_left;
 	return n;
 }
-extern struct rb_node *rb_last(const struct rb_root *);
+
+/*
+ * This function returns the last node (in sort order) of the tree.
+ */
+static inline struct rb_node *rb_last(const struct rb_root *root)
+{
+	struct rb_node	*n;
+
+	n = root->rb_node;
+	if (!n)
+		return NULL;
+	while (n->rb_right)
+		n = n->rb_right;
+	return n;
+}
 
 /* Postorder iteration - always visit the parent after its children */
 extern struct rb_node *rb_first_postorder(const struct rb_root *);

lib/rbtree.c

···
 }
 EXPORT_SYMBOL(__rb_insert_augmented);
 
-struct rb_node *rb_last(const struct rb_root *root)
-{
-	struct rb_node	*n;
-
-	n = root->rb_node;
-	if (!n)
-		return NULL;
-	while (n->rb_right)
-		n = n->rb_right;
-	return n;
-}
-EXPORT_SYMBOL(rb_last);
-
 struct rb_node *rb_next(const struct rb_node *node)
 {
 	struct rb_node *parent;

rust/helpers/rbtree.c

···
 {
 	return rb_first(root);
 }
+
+struct rb_node *rust_helper_rb_last(const struct rb_root *root)
+{
+	return rb_last(root);
+}