Applied gc patch to fix ORIGIN ICLASS method table leak

Based on the gc patch by ko1

https://github.com/ruby/ruby/commit/5922c954614e5947a548780bb3b894626affe6dd

include/mruby/class.h

@@ -49,8 +49,11 @@ mrb_class(mrb_state *mrb, mrb_value v)
   }
 }
 
-#define MRB_SET_INSTANCE_TT(c, tt) c->flags = ((c->flags & ~0xff) | (char)tt)
-#define MRB_INSTANCE_TT(c) (enum mrb_vtype)(c->flags & 0xff)
+// TODO: figure out where to put user flags
+#define MRB_FLAG_IS_ORIGIN (1 << 20)
+#define MRB_FLAG_IS_INSTANCE (0xFF)
+#define MRB_SET_INSTANCE_TT(c, tt) c->flags = ((c->flags & ~MRB_FLAG_IS_INSTANCE) | (char)tt)
+#define MRB_INSTANCE_TT(c) (enum mrb_vtype)(c->flags & MRB_FLAG_IS_INSTANCE)
 
 MRB_API struct RClass* mrb_define_class_id(mrb_state*, mrb_sym, struct RClass*);
 MRB_API struct RClass* mrb_define_module_id(mrb_state*, mrb_sym);

include/mruby/object.h

@@ -14,6 +14,8 @@
   struct RClass *c;\
   struct RBasic *gcnext
 
+#define MRB_FLAG_TEST(obj, flag) ((obj)->flags & flag)
+
 /* white: 011, black: 100, gray: 000 */
 #define MRB_GC_GRAY 0
 #define MRB_GC_WHITE_A 1

src/class.c

@@ -856,6 +856,7 @@ mrb_prepend_module(mrb_state *mrb, struct RClass *c, struct RClass *m)
   origin = c->origin;
   if (origin == c) {
     origin = (struct RClass*)mrb_obj_alloc(mrb, MRB_TT_ICLASS, c);
+    origin->flags |= MRB_FLAG_IS_ORIGIN;
     origin->origin = origin;
     origin->super = c->super;
     c->super = origin;

src/gc.c

@@ -498,7 +498,12 @@ gc_mark_children(mrb_state *mrb, struct RBasic *obj)
   mrb_gc_mark(mrb, (struct RBasic*)obj->c);
   switch (obj->tt) {
   case MRB_TT_ICLASS:
-    mrb_gc_mark(mrb, (struct RBasic*)((struct RClass*)obj)->super);
+    {
+      struct RClass *c = (struct RClass*)obj;
+      if (MRB_FLAG_TEST(c, MRB_FLAG_IS_ORIGIN))
+        mrb_gc_mark_mt(mrb, c);
+      mrb_gc_mark(mrb, (struct RBasic*)((struct RClass*)obj)->super);
+    }
     break;
 
   case MRB_TT_CLASS:
@@ -624,7 +629,10 @@ obj_free(mrb_state *mrb, struct RBasic *obj)
     mrb_gc_free_mt(mrb, (struct RClass*)obj);
     mrb_gc_free_iv(mrb, (struct RObject*)obj);
     break;
-
+  case MRB_TT_ICLASS:
+    if (MRB_FLAG_TEST(obj, MRB_FLAG_IS_ORIGIN))
+      mrb_gc_free_mt(mrb, (struct RClass*)obj);
+    break;
   case MRB_TT_ENV:
     {
       struct REnv *e = (struct REnv*)obj;