3 files changed, 17 insertions, 33 deletions
diff --git a/class.c b/class.c
index 1e436e6c96..ba57d8a39d 100644
--- a/class.c
+++ b/class.c
@@ -183,16 +183,6 @@ duplicate_classext_const_tbl(struct rb_id_table *src, VALUE klass)
     return dst;
 }
 
-static void
-duplicate_classext_superclasses(rb_classext_t *orig, rb_classext_t *copy)
-{
-    RCLASSEXT_SUPERCLASSES(copy) = RCLASSEXT_SUPERCLASSES(orig);
-    RCLASSEXT_SUPERCLASS_DEPTH(copy) = RCLASSEXT_SUPERCLASS_DEPTH(orig);
-    // the copy is always not the owner and the orig (or its parent class) will maintain the superclasses array
-    RCLASSEXT_SUPERCLASSES_OWNER(copy) = false;
-    RCLASSEXT_SUPERCLASSES_WITH_SELF(copy) = RCLASSEXT_SUPERCLASSES_WITH_SELF(orig);
-}
-
 static VALUE
 namespace_subclasses_tbl_key(const rb_namespace_t *ns)
 {
@@ -349,9 +339,6 @@ rb_class_duplicate_classext(rb_classext_t *orig, VALUE klass, const rb_namespace
 
     RCLASSEXT_CVC_TBL(ext) = duplicate_classext_id_table(RCLASSEXT_CVC_TBL(orig), dup_iclass);
 
-    // superclass_depth, superclasses
-    duplicate_classext_superclasses(orig, ext);
-
     // subclasses, subclasses_index
     duplicate_classext_subclasses(orig, ext);
 
@@ -832,11 +819,11 @@ rb_class_update_superclasses(VALUE klass)
     }
     else {
         superclasses = class_superclasses_including_self(super);
-        RCLASS_WRITE_SUPERCLASSES(super, super_depth, superclasses, true, true);
+        RCLASS_WRITE_SUPERCLASSES(super, super_depth, superclasses, true);
     }
 
     size_t depth = super_depth == RCLASS_MAX_SUPERCLASS_DEPTH ? super_depth : super_depth + 1;
-    RCLASS_WRITE_SUPERCLASSES(klass, depth, superclasses, false, false);
+    RCLASS_WRITE_SUPERCLASSES(klass, depth, superclasses, false);
 }
 
 void
diff --git a/gc.c b/gc.c
index 199e6b9788..aba799ab25 100644
--- a/gc.c
+++ b/gc.c
@@ -1238,7 +1238,8 @@ classext_free(rb_classext_t *ext, bool is_prime, VALUE namespace, void *arg)
         rb_id_table_free(tbl);
     }
     rb_class_classext_free_subclasses(ext, args->klass);
-    if (RCLASSEXT_SUPERCLASSES_OWNER(ext)) {
+    if (RCLASSEXT_SUPERCLASSES_WITH_SELF(ext)) {
+        RUBY_ASSERT(is_prime); // superclasses should only be used on prime
         xfree(RCLASSEXT_SUPERCLASSES(ext));
     }
     if (!is_prime) { // the prime classext will be freed with RClass
@@ -2293,10 +2294,9 @@ classext_superclasses_memsize(rb_classext_t *ext, bool prime, VALUE namespace, v
 {
     size_t *size = (size_t *)arg;
     size_t array_size;
-    if (RCLASSEXT_SUPERCLASSES_OWNER(ext)) {
-        array_size = RCLASSEXT_SUPERCLASS_DEPTH(ext);
-        if (RCLASSEXT_SUPERCLASSES_WITH_SELF(ext))
-            array_size += 1;
+    if (RCLASSEXT_SUPERCLASSES_WITH_SELF(ext)) {
+        RUBY_ASSERT(prime);
+        array_size = RCLASSEXT_SUPERCLASS_DEPTH(ext) + 1;
         *size += array_size * sizeof(VALUE);
     }
 }
@@ -3802,10 +3802,8 @@ update_subclasses(void *objspace, rb_classext_t *ext)
 static void
 update_superclasses(rb_objspace_t *objspace, rb_classext_t *ext)
 {
-    size_t array_size = RCLASSEXT_SUPERCLASS_DEPTH(ext);
-    if (RCLASSEXT_SUPERCLASSES_OWNER(ext)) {
-        if (RCLASSEXT_SUPERCLASSES_WITH_SELF(ext))
-            array_size += 1;
+    if (RCLASSEXT_SUPERCLASSES_WITH_SELF(ext)) {
+        size_t array_size = RCLASSEXT_SUPERCLASS_DEPTH(ext) + 1;
         for (size_t i = 0; i < array_size; i++) {
             UPDATE_IF_MOVED(objspace, RCLASSEXT_SUPERCLASSES(ext)[i]);
         }
diff --git a/internal/class.h b/internal/class.h
index 82f8f0e9dc..15530b8842 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -127,7 +127,6 @@ struct rb_classext_struct {
     bool shared_const_tbl : 1;
     bool iclass_is_origin : 1;
     bool iclass_origin_shared_mtbl : 1;
-    bool superclasses_owner : 1;
     bool superclasses_with_self : 1;
     VALUE classpath;
 };
@@ -198,7 +197,6 @@ static inline rb_classext_t * RCLASS_EXT_WRITABLE(VALUE obj);
 #define RCLASSEXT_SHARED_CONST_TBL(ext) (ext->shared_const_tbl)
 #define RCLASSEXT_ICLASS_IS_ORIGIN(ext) (ext->iclass_is_origin)
 #define RCLASSEXT_ICLASS_ORIGIN_SHARED_MTBL(ext) (ext->iclass_origin_shared_mtbl)
-#define RCLASSEXT_SUPERCLASSES_OWNER(ext) (ext->superclasses_owner)
 #define RCLASSEXT_SUPERCLASSES_WITH_SELF(ext) (ext->superclasses_with_self)
 #define RCLASSEXT_CLASSPATH(ext) (ext->classpath)
 
@@ -227,9 +225,6 @@ static inline void RCLASSEXT_SET_INCLUDER(rb_classext_t *ext, VALUE klass, VALUE
  * so always those should be writable.
  */
 #define RCLASS_CVC_TBL(c) (RCLASS_EXT_READABLE(c)->cvc_tbl)
-#define RCLASS_SUPERCLASS_DEPTH(c) (RCLASS_EXT_READABLE(c)->superclass_depth)
-#define RCLASS_SUPERCLASSES(c) (RCLASS_EXT_READABLE(c)->superclasses)
-#define RCLASS_SUPERCLASSES_WITH_SELF_P(c) (RCLASS_EXT_READABLE(c)->superclasses_with_self)
 #define RCLASS_SUBCLASSES_X(c) (RCLASS_EXT_READABLE(c)->subclasses)
 #define RCLASS_SUBCLASSES_FIRST(c) (RCLASS_EXT_READABLE(c)->subclasses->head->next)
 #define RCLASS_ORIGIN(c) (RCLASS_EXT_READABLE(c)->origin_)
@@ -240,6 +235,11 @@ static inline void RCLASSEXT_SET_INCLUDER(rb_classext_t *ext, VALUE klass, VALUE
 #define RCLASS_CLONED_P(c) (RCLASS_EXT_READABLE(c)->cloned)
 #define RCLASS_CLASSPATH(c) (RCLASS_EXT_READABLE(c)->classpath)
 
+// Superclasses can't be changed after initialization
+#define RCLASS_SUPERCLASS_DEPTH(c) (RCLASS_EXT_PRIME(c)->superclass_depth)
+#define RCLASS_SUPERCLASSES(c) (RCLASS_EXT_PRIME(c)->superclasses)
+#define RCLASS_SUPERCLASSES_WITH_SELF_P(c) (RCLASS_EXT_PRIME(c)->superclasses_with_self)
+
 // namespaces don't make changes on these refined_class/attached_object/includer
 #define RCLASS_REFINED_CLASS(c) (RCLASS_EXT_PRIME(c)->refined_class)
 #define RCLASS_ATTACHED_OBJECT(c) (RCLASS_EXT_PRIME(c)->as.singleton_class.attached_object)
@@ -270,7 +270,7 @@ static inline void RCLASS_WRITE_CC_TBL(VALUE klass, struct rb_id_table *table);
 static inline void RCLASS_SET_CVC_TBL(VALUE klass, struct rb_id_table *table);
 static inline void RCLASS_WRITE_CVC_TBL(VALUE klass, struct rb_id_table *table);
 
-static inline void RCLASS_WRITE_SUPERCLASSES(VALUE klass, size_t depth, VALUE *superclasses, bool owns_it, bool with_self);
+static inline void RCLASS_WRITE_SUPERCLASSES(VALUE klass, size_t depth, VALUE *superclasses, bool with_self);
 static inline void RCLASS_SET_SUBCLASSES(VALUE klass, rb_subclass_anchor_t *anchor);
 static inline void RCLASS_WRITE_NS_SUPER_SUBCLASSES(VALUE klass, rb_ns_subclasses_t *ns_subclasses);
 static inline void RCLASS_WRITE_NS_MODULE_SUBCLASSES(VALUE klass, rb_ns_subclasses_t *ns_subclasses);
@@ -714,14 +714,13 @@ RCLASS_SET_INCLUDER(VALUE iclass, VALUE klass)
 }
 
 static inline void
-RCLASS_WRITE_SUPERCLASSES(VALUE klass, size_t depth, VALUE *superclasses, bool owns_it, bool with_self)
+RCLASS_WRITE_SUPERCLASSES(VALUE klass, size_t depth, VALUE *superclasses, bool with_self)
 {
     RUBY_ASSERT(depth <= RCLASS_MAX_SUPERCLASS_DEPTH);
 
-    rb_classext_t *ext = RCLASS_EXT_WRITABLE(klass);
+    rb_classext_t *ext = RCLASS_EXT_PRIME(klass);
     RCLASSEXT_SUPERCLASS_DEPTH(ext) = depth;
     RCLASSEXT_SUPERCLASSES(ext) = superclasses;
-    RCLASSEXT_SUPERCLASSES_OWNER(ext) = owns_it;
     RCLASSEXT_SUPERCLASSES_WITH_SELF(ext) = with_self;
 }