Move `attached_object` into `rb_classext_struct`

Given that signleton classes don't have an allocator,
we can re-use these bytes to store the attached object
in `rb_classext_struct` without making it larger.

1 files changed, 1 insertions, 1 deletions

diff --git a/marshal.c b/marshal.c
index 78e5bde0a2..af952048af 100644
--- a/marshal.c
+++ b/marshal.c
@@ -523,7 +523,7 @@ hash_each(VALUE key, VALUE value, VALUE v)
 
 #define SINGLETON_DUMP_UNABLE_P(klass) \
     (rb_id_table_size(RCLASS_M_TBL(klass)) > 0 || \
-     rb_ivar_count(klass) > 1)
+     rb_ivar_count(klass) > 0)
 
 static void
 w_extended(VALUE klass, struct dump_arg *arg, int check)