copy method cache into new singleton class for regular object

Author: tmm1

class.c

@@ -507,6 +507,7 @@ make_singleton_class(VALUE obj)
 {
     VALUE orig_class = RBASIC(obj)->klass;
     VALUE klass = rb_class_boot(orig_class);
+    rb_method_cache_copy(orig_class, klass);
 
     FL_SET(klass, FL_SINGLETON);
     RBASIC_SET_CLASS(obj, klass);

internal.h

@@ -805,6 +805,7 @@ VALUE rb_extract_keywords(VALUE *orighash);
 /* vm_method.c */
 void Init_eval_method(void);
 int rb_method_defined_by(VALUE obj, ID mid, VALUE (*cfunc)(ANYARGS));
+void rb_method_cache_copy(VALUE from, VALUE to);
 
 /* miniprelude.c, prelude.c */
 void Init_prelude(void);

vm_method.c

@@ -113,6 +113,23 @@ rb_mcache_find(struct rb_meth_cache *cache, ID id)
     }
 }
 
+void
+rb_method_cache_copy(VALUE from, VALUE to)
+{
+    struct rb_meth_cache *from_cache = &RCLASS_EXT(from)->cache, *to_cache = &RCLASS_EXT(to)->cache;
+    if (!from_cache->size) return;
+
+    if (to_cache->entries)
+	xfree(to_cache->entries);
+    to_cache->capa = from_cache->capa;
+    to_cache->entries = xcalloc(to_cache->capa, sizeof(struct cache_entry));
+    if (from_cache->entries)
+	MEMCPY(to_cache->entries, from_cache->entries, struct cache_entry, from_cache->capa);
+    to_cache->size = from_cache->size;
+    to_cache->method_state = from_cache->method_state;
+    to_cache->class_serial = RCLASS_SERIAL(to);
+}
+
 #define ruby_running (GET_VM()->running)
 /* int ruby_running = 0; */