11 files changed, 233 insertions, 193 deletions

diff --git a/ChangeLog b/ChangeLog
index ceb8fceac7..c045242eb2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Fri Aug 28 11:45:33 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* method.h (rb_method_definition_t): split from rb_method_entry_
+	  to deal aliases.  [ruby-dev:39165]
+
+	* proc.c (struct METHOD): contains rb_method_entry_t copy.
+
 Fri Aug 28 10:21:30 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* iseq.c (iseq_mark): skip outdated cache entries.
diff --git a/class.c b/class.c
index c64cbe72db..1ffb61a46a 100644
--- a/class.c
+++ b/class.c
@@ -126,17 +126,14 @@ VALUE rb_iseq_clone(VALUE iseqval, VALUE newcbase);
 static int
 clone_method(ID mid, const rb_method_entry_t *me, struct clone_method_data *data)
 {
-    switch (me->type) {
-      case VM_METHOD_TYPE_ISEQ: {
-	  VALUE newiseqval = rb_iseq_clone(me->body.iseq->self, data->klass);
-	  rb_iseq_t *iseq;
-	  GetISeqPtr(newiseqval, iseq);
-	  rb_add_method(data->klass, mid, VM_METHOD_TYPE_ISEQ, iseq, me->flag);
-	  break;
-      }
-      default:
+    if (me->def && me->def->type == VM_METHOD_TYPE_ISEQ) {
+	VALUE newiseqval = rb_iseq_clone(me->def->body.iseq->self, data->klass);
+	rb_iseq_t *iseq;
+	GetISeqPtr(newiseqval, iseq);
+	rb_add_method(data->klass, mid, VM_METHOD_TYPE_ISEQ, iseq, me->flag);
+    }
+    else {
 	rb_add_method_me(data->klass, mid, me, me->flag);
-	break;
     }
     return ST_CONTINUE;
 }
@@ -683,7 +680,7 @@ method_entry(ID key, const rb_method_entry_t *me, st_table *list)
     }
 
     if (!st_lookup(list, key, 0)) {
-	if (!me || me->type == VM_METHOD_TYPE_UNDEF) {
+	if (UNDEFINED_METHOD_ENTRY_P(me)) {
 	    type = -1; /* none */
 	}
 	else {
diff --git a/eval.c b/eval.c
index d6d2b7afc7..7ba413bd49 100644
--- a/eval.c
+++ b/eval.c
@@ -693,7 +693,7 @@ frame_func_id(rb_control_frame_t *cfp)
 {
     rb_iseq_t *iseq = cfp->iseq;
     if (!iseq) {
-	return cfp->me->original_id;
+	return cfp->me->def->original_id;
     }
     while (iseq) {
 	if (RUBY_VM_IFUNC_P(iseq)) {
diff --git a/gc.c b/gc.c
index 113e13d51b..9a183a5d41 100644
--- a/gc.c
+++ b/gc.c
@@ -1377,13 +1377,16 @@ rb_mark_hash(st_table *tbl)
 static void
 mark_method_entry(rb_objspace_t *objspace, const rb_method_entry_t *me, int lev)
 {
+    const rb_method_definition_t *def = me->def;
+
     gc_mark(objspace, me->klass, lev);
-    switch (me->type) {
+    if (!def) return;
+    switch (def->type) {
       case VM_METHOD_TYPE_ISEQ:
-	gc_mark(objspace, me->body.iseq->self, lev);
+	gc_mark(objspace, def->body.iseq->self, lev);
 	break;
       case VM_METHOD_TYPE_BMETHOD:
-	gc_mark(objspace, me->body.proc, lev);
+	gc_mark(objspace, def->body.proc, lev);
 	break;
       default:
 	break; /* ignore */
@@ -1417,7 +1420,7 @@ mark_m_tbl(rb_objspace_t *objspace, st_table *tbl, int lev)
 static int
 free_method_entry_i(ID key, rb_method_entry_t *me, st_data_t data)
 {
-    xfree(me);
+    rb_free_method_entry(me);
     return ST_CONTINUE;
 }
 
diff --git a/method.h b/method.h
index 0185c059b5..e6d4fab8b3 100644
--- a/method.h
+++ b/method.h
@@ -49,12 +49,9 @@ typedef struct rb_method_cfunc_struct {
 
 typedef struct rb_iseq_struct rb_iseq_t;
 
-typedef struct rb_method_entry_struct {
-    rb_method_flag_t flag;
+typedef struct rb_method_definition_struct {
     rb_method_type_t type; /* method type */
-    ID called_id;
     ID original_id;
-    VALUE klass;                    /* should be mark */
     union {
 	rb_iseq_t *iseq;            /* should be mark */
 	rb_method_cfunc_t cfunc;
@@ -66,13 +63,23 @@ typedef struct rb_method_entry_struct {
 	} optimize_type;
     } body;
     int alias_count;
+} rb_method_definition_t;
+
+typedef struct rb_method_entry_struct {
+    rb_method_flag_t flag;
+    rb_method_definition_t *def;
+    ID called_id;
+    VALUE klass;                    /* should be mark */
 } rb_method_entry_t;
 
+#define UNDEFINED_METHOD_ENTRY_P(me) (!(me) || !(me)->def || (me)->def->type == VM_METHOD_TYPE_UNDEF)
+
 void rb_add_method_cfunc(VALUE klass, ID mid, VALUE (*func)(ANYARGS), int argc, rb_method_flag_t noex);
 rb_method_entry_t *rb_add_method(VALUE klass, ID mid, rb_method_type_t type, void *option, rb_method_flag_t noex);
-void rb_add_method_me(VALUE klass, ID mid, const rb_method_entry_t *, rb_method_flag_t noex);
+rb_method_entry_t *rb_add_method_me(VALUE klass, ID mid, const rb_method_entry_t *, rb_method_flag_t noex);
 rb_method_entry_t *rb_method_entry(VALUE klass, ID id);
 int rb_method_entry_arity(const rb_method_entry_t *me);
 void rb_gc_mark_method_entry(const rb_method_entry_t *me);
+void rb_free_method_entry(rb_method_entry_t *me);
 
 #endif /* METHOD_H */
diff --git a/proc.c b/proc.c
index 15ddcd2729..39a66976c1 100644
--- a/proc.c
+++ b/proc.c
@@ -16,7 +16,7 @@ struct METHOD {
     VALUE recv;
     VALUE rclass;
     ID id;
-    rb_method_entry_t *me;
+    rb_method_entry_t me;
 };
 
 VALUE rb_cUnboundMethod;
@@ -843,7 +843,18 @@ bm_mark(void *ptr)
     struct METHOD *data = ptr;
     rb_gc_mark(data->rclass);
     rb_gc_mark(data->recv);
-    rb_gc_mark_method_entry(data->me);
+    rb_gc_mark_method_entry(&data->me);
+}
+
+static void
+bm_free(void *ptr)
+{
+    struct METHOD *data = ptr;
+    rb_method_definition_t *def = data->me.def;
+    if (def->alias_count == 0)
+	xfree(def);
+    else if (def->alias_count > 0)
+	def->alias_count--;
 }
 
 static size_t
@@ -855,7 +866,7 @@ bm_memsize(void *ptr)
 static const rb_data_type_t method_data_type = {
     "method",
     bm_mark,
-    RUBY_TYPED_DEFAULT_FREE,
+    bm_free,
     bm_memsize,
 };
 
@@ -873,18 +884,20 @@ mnew(VALUE klass, VALUE obj, ID id, VALUE mclass, int scope)
     ID rid = id;
     struct METHOD *data;
     rb_method_entry_t *me;
+    rb_method_definition_t *def;
 
   again:
     me = rb_method_entry(klass, id);
-    if (!me) {
+    if (UNDEFINED_METHOD_ENTRY_P(me)) {
 	rb_print_undef(klass, id, 0);
     }
+    def = me->def;
     if (scope && (me->flag & NOEX_MASK) != NOEX_PUBLIC) {
-	rb_print_undef(rclass, me->original_id, (int)(me->flag & NOEX_MASK));
+	rb_print_undef(rclass, def->original_id, (int)(me->flag & NOEX_MASK));
     }
-    if (me->type == VM_METHOD_TYPE_ZSUPER) {
+    if (def->type == VM_METHOD_TYPE_ZSUPER) {
 	klass = RCLASS_SUPER(me->klass);
-	id = me->original_id;
+	id = def->original_id;
 	goto again;
     }
 
@@ -904,7 +917,8 @@ mnew(VALUE klass, VALUE obj, ID id, VALUE mclass, int scope)
     data->recv = obj;
     data->rclass = rclass;
     data->id = rid;
-    data->me = me;
+    data->me = *me;
+    if (def) def->alias_count++;
 
     OBJ_INFECT(method, klass);
 
@@ -959,7 +973,7 @@ method_eq(VALUE method, VALUE other)
     m1 = (struct METHOD *)DATA_PTR(method);
     m2 = (struct METHOD *)DATA_PTR(other);
 
-    if (!rb_method_entry_eq(m1->me, m2->me) ||
+    if (!rb_method_entry_eq(&m1->me, &m2->me) ||
 	m1->rclass != m2->rclass ||
 	m1->recv != m2->recv) {
 	return Qfalse;
@@ -984,7 +998,7 @@ method_hash(VALUE method)
     TypedData_Get_Struct(method, struct METHOD, &method_data_type, m);
     hash =  (long)m->rclass;
     hash ^= (long)m->recv;
-    hash ^= (long)m->me;
+    hash ^= (long)m->me.def;
 
     return INT2FIX(hash);
 }
@@ -1010,6 +1024,7 @@ method_unbind(VALUE obj)
     data->recv = Qundef;
     data->id = orig->id;
     data->me = orig->me;
+    if (orig->me.def) orig->me.def->alias_count++;
     data->rclass = orig->rclass;
     OBJ_INFECT(method, obj);
 
@@ -1061,7 +1076,7 @@ method_owner(VALUE obj)
     struct METHOD *data;
 
     TypedData_Get_Struct(obj, struct METHOD, &method_data_type, data);
-    return data->me->klass;
+    return data->me.klass;
 }
 
 /*
@@ -1223,7 +1238,7 @@ rb_mod_define_method(int argc, VALUE *argv, VALUE mod)
 			 rb_class2name(rclass));
 	    }
 	}
-	rb_add_method_me(mod, id, method->me, noex);
+	rb_add_method_me(mod, id, &method->me, noex);
     }
     else if (rb_obj_is_proc(body)) {
 	rb_proc_t *proc;
@@ -1294,6 +1309,7 @@ method_clone(VALUE self)
     clone = TypedData_Make_Struct(CLASS_OF(self), struct METHOD, &method_data_type, data);
     CLONESETUP(clone, self);
     *data = *orig;
+    if (data->me.def) data->me.def->alias_count++;
 
     return clone;
 }
@@ -1336,7 +1352,7 @@ rb_method_call(int argc, VALUE *argv, VALUE method)
 			 const rb_method_entry_t *me);
 
 	PASS_PASSED_BLOCK_TH(th);
-	result = rb_vm_call(th, data->recv, data->id,  argc, argv, data->me);
+	result = rb_vm_call(th, data->recv, data->id,  argc, argv, &data->me);
     }
     POP_TAG();
     if (safe >= 0)
@@ -1456,6 +1472,7 @@ umethod_bind(VALUE method, VALUE recv)
 
     method = TypedData_Make_Struct(rb_cMethod, struct METHOD, &method_data_type, bound);
     *bound = *data;
+    if (bound->me.def) bound->me.def->alias_count++;
     bound->recv = recv;
     bound->rclass = CLASS_OF(recv);
 
@@ -1465,11 +1482,13 @@ umethod_bind(VALUE method, VALUE recv)
 int
 rb_method_entry_arity(const rb_method_entry_t *me)
 {
-    switch (me->type) {
+    const rb_method_definition_t *def = me->def;
+    if (!def) return 0;
+    switch (def->type) {
       case VM_METHOD_TYPE_CFUNC:
-	if (me->body.cfunc.argc < 0)
+	if (def->body.cfunc.argc < 0)
 	    return -1;
-	return check_argc(me->body.cfunc.argc);
+	return check_argc(def->body.cfunc.argc);
       case VM_METHOD_TYPE_ZSUPER:
 	return -1;
       case VM_METHOD_TYPE_ATTRSET:
@@ -1477,9 +1496,9 @@ rb_method_entry_arity(const rb_method_entry_t *me)
       case VM_METHOD_TYPE_IVAR:
 	return 0;
       case VM_METHOD_TYPE_BMETHOD:
-	return rb_proc_arity(me->body.proc);
+	return rb_proc_arity(def->body.proc);
       case VM_METHOD_TYPE_ISEQ: {
-	rb_iseq_t *iseq = me->body.iseq;
+	rb_iseq_t *iseq = def->body.iseq;
 	if (iseq->arg_rest == -1 && iseq->arg_opts == 0) {
 	    return iseq->argc;
 	}
@@ -1491,7 +1510,7 @@ rb_method_entry_arity(const rb_method_entry_t *me)
       case VM_METHOD_TYPE_NOTIMPLEMENTED:
 	return 0;
       case VM_METHOD_TYPE_OPTIMIZED: {
-	switch (me->body.optimize_type) {
+	switch (def->body.optimize_type) {
 	  case OPTIMIZED_METHOD_TYPE_SEND:
 	    return -1;
 	  default:
@@ -1499,7 +1518,7 @@ rb_method_entry_arity(const rb_method_entry_t *me)
 	}
       }
     }
-    rb_bug("rb_method_entry_arity: invalid method entry type (%d)", me->type);
+    rb_bug("rb_method_entry_arity: invalid method entry type (%d)", def->type);
 }
 
 /*
@@ -1548,7 +1567,7 @@ method_arity(VALUE method)
     struct METHOD *data;
 
     TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);
-    return rb_method_entry_arity(data->me);
+    return rb_method_entry_arity(&data->me);
 }
 
 int
@@ -1568,16 +1587,16 @@ rb_iseq_t *
 rb_method_get_iseq(VALUE method)
 {
     struct METHOD *data;
-    rb_method_entry_t *me;
+    rb_method_definition_t *def;
 
     TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);
-    me = data->me;
+    def = data->me.def;
 
-    switch (me->type) {
+    switch (def->type) {
       case VM_METHOD_TYPE_BMETHOD:
-	return get_proc_iseq(me->body.proc, 0);
+	return get_proc_iseq(def->body.proc, 0);
       case VM_METHOD_TYPE_ISEQ:
-	return me->body.iseq;
+	return def->body.iseq;
       default:
 	return 0;
     }
@@ -1638,11 +1657,11 @@ method_inspect(VALUE method)
     rb_str_buf_cat2(str, s);
     rb_str_buf_cat2(str, ": ");
 
-    if (FL_TEST(data->me->klass, FL_SINGLETON)) {
-	VALUE v = rb_iv_get(data->me->klass, "__attached__");
+    if (FL_TEST(data->me.klass, FL_SINGLETON)) {
+	VALUE v = rb_iv_get(data->me.klass, "__attached__");
 
 	if (data->recv == Qundef) {
-	    rb_str_buf_append(str, rb_inspect(data->me->klass));
+	    rb_str_buf_append(str, rb_inspect(data->me.klass));
 	}
 	else if (data->recv == v) {
 	    rb_str_buf_append(str, rb_inspect(v));
@@ -1658,15 +1677,15 @@ method_inspect(VALUE method)
     }
     else {
 	rb_str_buf_cat2(str, rb_class2name(data->rclass));
-	if (data->rclass != data->me->klass) {
+	if (data->rclass != data->me.klass) {
 	    rb_str_buf_cat2(str, "(");
-	    rb_str_buf_cat2(str, rb_class2name(data->me->klass));
+	    rb_str_buf_cat2(str, rb_class2name(data->me.klass));
 	    rb_str_buf_cat2(str, ")");
 	}
     }
     rb_str_buf_cat2(str, sharp);
-    rb_str_append(str, rb_id2str(data->me->original_id));
-    if (data->me->type == VM_METHOD_TYPE_NOTIMPLEMENTED) {
+    rb_str_append(str, rb_id2str(data->me.def->original_id));
+    if (data->me.def->type == VM_METHOD_TYPE_NOTIMPLEMENTED) {
         rb_str_buf_cat2(str, " (not-implemented)");
     }
     rb_str_buf_cat2(str, ">");
diff --git a/vm.c b/vm.c
index c9c10dccbe..4af968653d 100644
--- a/vm.c
+++ b/vm.c
@@ -735,7 +735,7 @@ vm_backtrace_each(rb_thread_t *th, int lev, rb_backtrace_iter_func *iter, void *
 	}
 	else if (RUBYVM_CFUNC_FRAME_P(cfp)) {
 	    if (NIL_P(file)) file = rb_str_new_cstr("ruby");
-	    if ((*iter)(arg, file, line_no, rb_id2str(cfp->me->original_id))) break;
+	    if ((*iter)(arg, file, line_no, rb_id2str(cfp->me->def->original_id))) break;
 	}
 	cfp = RUBY_VM_NEXT_CONTROL_FRAME(cfp);
     }
@@ -937,7 +937,7 @@ static void
 rb_vm_check_redefinition_opt_method(const rb_method_entry_t *me)
 {
     VALUE bop;
-    if (me->type == VM_METHOD_TYPE_CFUNC) {
+    if (!me->def || me->def->type == VM_METHOD_TYPE_CFUNC) {
 	if (st_lookup(vm_opt_method_table, (st_data_t)me, &bop)) {
 	    ruby_vm_redefined_flag[bop] = 1;
 	}
@@ -948,8 +948,8 @@ static void
 add_opt_method(VALUE klass, ID mid, VALUE bop)
 {
     rb_method_entry_t *me;
-    if (st_lookup(RCLASS_M_TBL(klass), mid, (void *)&me) &&
-	me->type == VM_METHOD_TYPE_CFUNC) {
+    if (st_lookup(RCLASS_M_TBL(klass), mid, (void *)&me) && me->def &&
+	me->def->type == VM_METHOD_TYPE_CFUNC) {
 	st_insert(vm_opt_method_table, (st_data_t)me, (st_data_t)bop);
     }
     else {
@@ -1338,7 +1338,7 @@ rb_thread_method_id_and_class(rb_thread_t *th,
     rb_control_frame_t *cfp = th->cfp;
     rb_iseq_t *iseq = cfp->iseq;
     if (!iseq) {
-	if (idp) *idp = cfp->me->original_id;
+	if (idp) *idp = cfp->me->def->original_id;
 	if (klassp) *klassp = cfp->me->klass;
 	return 1;
     }
@@ -1382,10 +1382,10 @@ rb_thread_current_status(const rb_thread_t *th)
 			     file, line_no, RSTRING_PTR(iseq->name));
 	}
     }
-    else if (cfp->me->original_id) {
+    else if (cfp->me->def->original_id) {
 	str = rb_sprintf("`%s#%s' (cfunc)",
 			 RSTRING_PTR(rb_class_name(cfp->me->klass)),
-			 rb_id2name(cfp->me->original_id));
+			 rb_id2name(cfp->me->def->original_id));
     }
 
     return str;
diff --git a/vm_dump.c b/vm_dump.c
index 0759a93fe3..3addd9ee32 100644
--- a/vm_dump.c
+++ b/vm_dump.c
@@ -113,8 +113,8 @@ control_frame_dump(rb_thread_t *th, rb_control_frame_t *cfp)
 	}
     }
     else if (cfp->me) {
-	iseq_name = rb_id2name(cfp->me->original_id);
-	snprintf(posbuf, MAX_POSBUF, ":%s", rb_id2name(cfp->me->original_id));
+	iseq_name = rb_id2name(cfp->me->def->original_id);
+	snprintf(posbuf, MAX_POSBUF, ":%s", iseq_name);
 	line = -1;
     }
 
diff --git a/vm_eval.c b/vm_eval.c
index 8784b88d7b..801070bed6 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -33,17 +33,19 @@ static inline VALUE
 vm_call0(rb_thread_t* th, VALUE recv, VALUE id, int argc, const VALUE *argv,
 	 const rb_method_entry_t *me)
 {
+    const rb_method_definition_t *def = me->def;
     VALUE val;
     VALUE klass = me->klass;
     const rb_block_t *blockptr = 0;
 
+    if (!def) return Qnil;
     if (th->passed_block) {
 	blockptr = th->passed_block;
 	th->passed_block = 0;
     }
 
   again:
-    switch (me->type) {
+    switch (def->type) {
       case VM_METHOD_TYPE_ISEQ: {
 	rb_control_frame_t *reg_cfp;
 	int i;
@@ -71,7 +73,7 @@ vm_call0(rb_thread_t* th, VALUE recv, VALUE id, int argc, const VALUE *argv,
 			      recv, (VALUE)blockptr, 0, reg_cfp->sp, 0, 1);
 
 	    cfp->me = me;
-	    val = call_cfunc(me->body.cfunc.func, recv, me->body.cfunc.argc, argc, argv);
+	    val = call_cfunc(def->body.cfunc.func, recv, def->body.cfunc.argc, argc, argv);
 
 	    if (reg_cfp != th->cfp + 1) {
 		rb_bug("cfp consistency error - call0");
@@ -85,14 +87,14 @@ vm_call0(rb_thread_t* th, VALUE recv, VALUE id, int argc, const VALUE *argv,
 	if (argc != 1) {
 	    rb_raise(rb_eArgError, "wrong number of arguments (%d for 1)", argc);
 	}
-	val = rb_ivar_set(recv, me->body.attr_id, argv[0]);
+	val = rb_ivar_set(recv, def->body.attr_id, argv[0]);
 	break;
       }
       case VM_METHOD_TYPE_IVAR: {
 	if (argc != 0) {
 	    rb_raise(rb_eArgError, "wrong number of arguments (%d for 0)", argc);
 	}
-	val = rb_attr_get(recv, me->body.attr_id);
+	val = rb_attr_get(recv, def->body.attr_id);
 	break;
       }
       case VM_METHOD_TYPE_BMETHOD: {
@@ -105,10 +107,11 @@ vm_call0(rb_thread_t* th, VALUE recv, VALUE id, int argc, const VALUE *argv,
 	    return method_missing(recv, id, argc, argv, 0);
 	}
 	RUBY_VM_CHECK_INTS();
+	if (!(def = me->def)) return Qnil;
 	goto again;
       }
       case VM_METHOD_TYPE_OPTIMIZED: {
-	switch (me->body.optimize_type) {
+	switch (def->body.optimize_type) {
 	  case OPTIMIZED_METHOD_TYPE_SEND:
 	    val = send_internal(argc, argv, recv, NOEX_NOSUPER | NOEX_PRIVATE);
 	    break;
@@ -119,14 +122,14 @@ vm_call0(rb_thread_t* th, VALUE recv, VALUE id, int argc, const VALUE *argv,
 	    break;
 	  }
 	  default:
-	    rb_bug("vm_call0: unsupported optimized method type (%d)", me->body.optimize_type);
+	    rb_bug("vm_call0: unsupported optimized method type (%d)", def->body.optimize_type);
 	    val = Qundef;
 	    break;
 	}
 	break;
       }
       default:
-	rb_bug("vm_call0: unsupported method type (%d)", me->type);
+	rb_bug("vm_call0: unsupported method type (%d)", def->type);
 	val = Qundef;
     }
     RUBY_VM_CHECK_INTS();
@@ -156,7 +159,7 @@ vm_call_super(rb_thread_t *th, int argc, const VALUE *argv)
 	if (klass == 0) {
 	    klass = vm_search_normal_superclass(cfp->me->klass, recv);
 	}
-	id = cfp->me->original_id;
+	id = cfp->me->def->original_id;
     }
     else {
 	rb_bug("vm_call_super: should not be reached");
@@ -212,14 +215,14 @@ rb_call0(VALUE recv, ID mid, int argc, const VALUE *argv,
     ent = cache + EXPR1(klass, mid);
 
     if (ent->mid == mid && ent->klass == klass) {
-	if (!ent->me) {
-	  return method_missing(recv, mid, argc, argv,
-				scope == CALL_VCALL ? NOEX_VCALL : 0);
-	}
 	me = ent->me;
+	if (UNDEFINED_METHOD_ENTRY_P(me)) {
+	    return method_missing(recv, mid, argc, argv,
+				  scope == CALL_VCALL ? NOEX_VCALL : 0);
+	}
 	klass = me->klass;
     }
-    else if ((me = rb_method_entry(klass, mid)) != 0) {
+    else if ((me = rb_method_entry(klass, mid)) != 0 && me->def) {
 	klass = me->klass;
     }
     else {
@@ -230,7 +233,7 @@ rb_call0(VALUE recv, ID mid, int argc, const VALUE *argv,
 			      scope == CALL_VCALL ? NOEX_VCALL : 0);
     }
 
-    oid = me->original_id;
+    oid = me->def->original_id;
     noex = me->flag;
 
     if (oid != idMethodMissing) {
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 5da3f1783b..117bf95790 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -361,15 +361,14 @@ vm_call_cfunc(rb_thread_t *th, rb_control_frame_t *reg_cfp,
 {
     VALUE val = 0;
     int state = 0;
+    const rb_method_definition_t *def = me->def;
     VALUE klass = me->klass;
     ID id = me->called_id;
 
     EXEC_EVENT_HOOK(th, RUBY_EVENT_C_CALL, recv, id, klass);
 
     TH_PUSH_TAG(th);
-#if defined(__cplusplus) || (__STDC_VERSION__ >= 199901L)
-    // TODO: fix me.  separate event
-#endif
+    /* TODO: fix me.  separate event */
     if (th->event_flags & (RUBY_EVENT_C_RETURN | RUBY_EVENT_VM)) {
 	state = TH_EXEC_TAG();
     }
@@ -384,7 +383,7 @@ vm_call_cfunc(rb_thread_t *th, rb_control_frame_t *reg_cfp,
 	cfp->me = me;
 	reg_cfp->sp -= num + 1;
 
-	val = call_cfunc(me->body.cfunc.func, recv, (int)me->body.cfunc.argc, num, reg_cfp->sp + 1);
+	val = call_cfunc(def->body.cfunc.func, recv, (int)def->body.cfunc.argc, num, reg_cfp->sp + 1);
 
 	if (reg_cfp != th->cfp + 1) {
 	    rb_bug("cfp consistency error - send");
@@ -410,7 +409,7 @@ vm_call_bmethod(rb_thread_t *th, VALUE recv, int argc, const VALUE *argv,
     /* control block frame */
     (cfp-2)->me = me;
 
-    GetProcPtr(me->body.proc, proc);
+    GetProcPtr(me->def->body.proc, proc);
     val = rb_vm_invoke_proc(th, proc, recv, argc, argv, blockptr);
     return val;
 }
@@ -443,7 +442,7 @@ vm_setup_method(rb_thread_t *th, rb_control_frame_t *cfp,
 {
     int opt_pc, i;
     VALUE *sp, *rsp = cfp->sp - argc;
-    rb_iseq_t *iseq = me->body.iseq;
+    rb_iseq_t *iseq = me->def->body.iseq;
 
     VM_CALLEE_SETUP_ARG(opt_pc, th, iseq, argc, rsp, &blockptr);
 
@@ -502,7 +501,7 @@ vm_call_method(rb_thread_t *th, rb_control_frame_t *cfp,
     if (me != 0) {
 	if ((me->flag == 0)) {
 	  normal_method_dispatch:
-	    switch (me->type) {
+	    switch (me->def->type) {
 	      case VM_METHOD_TYPE_ISEQ:{
 		vm_setup_method(th, cfp, recv, num, blockptr, flag, me);
 		return Qundef;
@@ -516,7 +515,7 @@ vm_call_method(rb_thread_t *th, rb_control_frame_t *cfp,
 		if (num != 1) {
 		    rb_raise(rb_eArgError, "wrong number of arguments (%d for 1)", num);
 		}
-		val = rb_ivar_set(recv, me->body.attr_id, *(cfp->sp - 1));
+		val = rb_ivar_set(recv, me->def->body.attr_id, *(cfp->sp - 1));
 		cfp->sp -= 2;
 		break;
 	      }
@@ -524,7 +523,7 @@ vm_call_method(rb_thread_t *th, rb_control_frame_t *cfp,
 		if (num != 0) {
 		    rb_raise(rb_eArgError, "wrong number of arguments (%d for 0)", num);
 		}
-		val = rb_attr_get(recv, me->body.attr_id);
+		val = rb_attr_get(recv, me->def->body.attr_id);
 		cfp->sp -= 1;
 		break;
 	      }
@@ -547,7 +546,7 @@ vm_call_method(rb_thread_t *th, rb_control_frame_t *cfp,
 		}
 	      }
 	      case VM_METHOD_TYPE_OPTIMIZED:{
-		switch (me->body.optimize_type) {
+		switch (me->def->body.optimize_type) {
 		  case OPTIMIZED_METHOD_TYPE_SEND: {
 		    rb_control_frame_t *reg_cfp = cfp;
 		    rb_num_t i = num - 1;
@@ -583,12 +582,12 @@ vm_call_method(rb_thread_t *th, rb_control_frame_t *cfp,
 		  }
 		  default:
 		    rb_bug("eval_invoke_method: unsupported optimized method type (%d)",
-			   me->body.optimize_type);
+			   me->def->body.optimize_type);
 		}
 		break;
 	      }
 	      default:{
-		rb_bug("eval_invoke_method: unsupported method type (%d)", me->type);
+		rb_bug("eval_invoke_method: unsupported method type (%d)", me->def->type);
 		break;
 	      }
 	    }
@@ -1309,7 +1308,7 @@ vm_search_superclass(rb_control_frame_t *reg_cfp, rb_iseq_t *ip,
 	    }
 	}
 
-	id = lcfp->me->original_id;
+	id = lcfp->me->def->original_id;
 	klass = vm_search_normal_superclass(lcfp->me->klass, recv);
     }
     else {
@@ -1531,8 +1530,8 @@ vm_expandarray(rb_control_frame_t *cfp, VALUE ary, rb_num_t num, int flag)
 static inline int
 check_cfunc(const rb_method_entry_t *me, VALUE (*func)())
 {
-    if (me && me->type == VM_METHOD_TYPE_CFUNC &&
-	me->body.cfunc.func == func) {
+    if (me && me->def->type == VM_METHOD_TYPE_CFUNC &&
+	me->def->body.cfunc.func == func) {
 	return 1;
     }
     else {
diff --git a/vm_method.c b/vm_method.c
index d7111935b0..1091eadbcd 100644
--- a/vm_method.c
+++ b/vm_method.c
@@ -126,8 +126,23 @@ rb_add_method_cfunc(VALUE klass, ID mid, VALUE (*func)(ANYARGS), int argc, rb_me
     }
 }
 
-rb_method_entry_t *
-rb_add_method(VALUE klass, ID mid, rb_method_type_t type, void *opts, rb_method_flag_t noex)
+void
+rb_free_method_entry(rb_method_entry_t *me)
+{
+    rb_method_definition_t *def = me->def;
+
+    if (def) {
+	if (def->alias_count == 0)
+	    xfree(def);
+	else if (def->alias_count > 0)
+	    def->alias_count--;
+	me->def = 0;
+    }
+    xfree(me);
+}
+
+static rb_method_entry_t *
+rb_add_method_def(VALUE klass, ID mid, rb_method_type_t type, rb_method_definition_t *def, rb_method_flag_t noex)
 {
     rb_method_entry_t *me;
     st_table *mtbl;
@@ -156,60 +171,34 @@ rb_add_method(VALUE klass, ID mid, rb_method_type_t type, void *opts, rb_method_
     if (OBJ_FROZEN(klass)) {
 	rb_error_frozen("class/module");
     }
-    rb_clear_cache_by_id(mid);
-
-    me = ALLOC(rb_method_entry_t);
-    me->type = type;
-    me->original_id = me->called_id = mid;
-    me->klass = klass;
-    me->flag = NOEX_WITH_SAFE(noex);
-    me->alias_count = 0;
-
-    switch (type) {
-      case VM_METHOD_TYPE_ISEQ:
-	me->body.iseq = (rb_iseq_t *)opts;
-	break;
-      case VM_METHOD_TYPE_CFUNC:
-	me->body.cfunc = *(rb_method_cfunc_t *)opts;
-	break;
-      case VM_METHOD_TYPE_ATTRSET:
-      case VM_METHOD_TYPE_IVAR:
-	me->body.attr_id = (ID)opts;
-	break;
-      case VM_METHOD_TYPE_BMETHOD:
-	me->body.proc = (VALUE)opts;
-	break;
-      case VM_METHOD_TYPE_NOTIMPLEMENTED:
-	me->body.cfunc.func = rb_f_notimplement;
-	me->body.cfunc.argc = -1;
-	break;
-      case VM_METHOD_TYPE_OPTIMIZED:
-	me->body.optimize_type = (enum method_optimized_type)opts;
-	break;
-      case VM_METHOD_TYPE_ZSUPER:
-      case VM_METHOD_TYPE_UNDEF:
-	break;
-      default:
-	rb_bug("rb_add_method: unsupported method type (%d)\n", type);
-    }
 
     mtbl = RCLASS_M_TBL(klass);
 
     /* check re-definition */
     if (st_lookup(mtbl, mid, &data)) {
 	rb_method_entry_t *old_me = (rb_method_entry_t *)data;
+	rb_method_definition_t *old_def = old_me->def;
+
+	if (old_def == def) return old_me;
 	rb_vm_check_redefinition_opt_method(old_me);
 
 	if (RTEST(ruby_verbose) &&
-	    old_me->alias_count == 0 &&
-	    old_me->type != VM_METHOD_TYPE_UNDEF) {
+	    old_def->alias_count == 0 &&
+	    old_def->type != VM_METHOD_TYPE_UNDEF) {
 	    rb_warning("method redefined; discarding old %s", rb_id2name(mid));
 	}
-#if defined(__cplusplus) || (__STDC_VERSION__ >= 199901L)
-	// TODO: free old_me
-#endif
+	rb_free_method_entry(old_me);
     }
 
+    rb_clear_cache_by_id(mid);
+
+    me = ALLOC(rb_method_entry_t);
+    me->flag = NOEX_WITH_SAFE(noex);
+    me->called_id = mid;
+    me->klass = klass;
+    me->def = def;
+    if (def) def->alias_count++;
+
     /* check mid */
     if (klass == rb_cObject && mid == idInitialize) {
 	rb_warn("redefining Object#initialize may cause infinite loop");
@@ -235,6 +224,52 @@ rb_add_method(VALUE klass, ID mid, rb_method_type_t type, void *opts, rb_method_
     return me;
 }
 
+rb_method_entry_t *
+rb_add_method(VALUE klass, ID mid, rb_method_type_t type, void *opts, rb_method_flag_t noex)
+{
+    rb_method_entry_t *me = rb_add_method_def(klass, mid, type, 0, noex);
+    rb_method_definition_t *def = ALLOC(rb_method_definition_t);
+    me->def = def;
+    def->type = type;
+    def->original_id = mid;
+    def->alias_count = 0;
+    switch (type) {
+      case VM_METHOD_TYPE_ISEQ:
+	def->body.iseq = (rb_iseq_t *)opts;
+	break;
+      case VM_METHOD_TYPE_CFUNC:
+	def->body.cfunc = *(rb_method_cfunc_t *)opts;
+	break;
+      case VM_METHOD_TYPE_ATTRSET:
+      case VM_METHOD_TYPE_IVAR:
+	def->body.attr_id = (ID)opts;
+	break;
+      case VM_METHOD_TYPE_BMETHOD:
+	def->body.proc = (VALUE)opts;
+	break;
+      case VM_METHOD_TYPE_NOTIMPLEMENTED:
+	def->body.cfunc.func = rb_f_notimplement;
+	def->body.cfunc.argc = -1;
+	break;
+      case VM_METHOD_TYPE_OPTIMIZED:
+	def->body.optimize_type = (enum method_optimized_type)opts;
+	break;
+      case VM_METHOD_TYPE_ZSUPER:
+      case VM_METHOD_TYPE_UNDEF:
+	break;
+      default:
+	rb_bug("rb_add_method: unsupported method type (%d)\n", type);
+    }
+    return me;
+}
+
+rb_method_entry_t *
+rb_add_method_me(VALUE klass, ID mid, const rb_method_entry_t *me, rb_method_flag_t noex)
+{
+    rb_method_type_t type = me->def ? me->def->type : VM_METHOD_TYPE_UNDEF;
+    return rb_add_method_def(klass, mid, type, me->def, noex);
+}
+
 void
 rb_define_alloc_func(VALUE klass, VALUE (*func)(VALUE))
 {
@@ -257,8 +292,8 @@ rb_get_alloc_func(VALUE klass)
     Check_Type(klass, T_CLASS);
     me = rb_method_entry(CLASS_OF(klass), ID_ALLOCATOR);
 
-    if (me && me->type == VM_METHOD_TYPE_CFUNC) {
-	return (rb_alloc_func_t)me->body.cfunc.func;
+    if (me && me->def && me->def->type == VM_METHOD_TYPE_CFUNC) {
+	return (rb_alloc_func_t)me->def->body.cfunc.func;
     }
     else {
 	return 0;
@@ -299,7 +334,7 @@ rb_get_method_entry(VALUE klass, ID id)
 	ent = cache + EXPR1(klass, id);
 	ent->klass = klass;
 
-	if (!me || me->type == VM_METHOD_TYPE_UNDEF) {
+	if (UNDEFINED_METHOD_ENTRY_P(me)) {
 	    ent->mid = id;
 	    ent->me = 0;
 	    me = 0;
@@ -346,7 +381,7 @@ rb_remove_method_id(VALUE klass, ID mid)
 
     if (st_lookup(RCLASS_M_TBL(klass), mid, &data)) {
 	me = (rb_method_entry_t *)data;
-	if (!me || me->type == VM_METHOD_TYPE_UNDEF) {
+	if (!me || (me->def && me->def->type == VM_METHOD_TYPE_UNDEF)) {
 	    me = 0;
 	}
 	else {
@@ -360,6 +395,7 @@ rb_remove_method_id(VALUE klass, ID mid)
 
     rb_vm_check_redefinition_opt_method(me);
     rb_clear_cache_for_undef(klass, mid);
+    rb_free_method_entry(me);
 
     if (FL_TEST(klass, FL_SINGLETON)) {
 	rb_funcall(rb_iv_get(klass, "__attached__"), singleton_removed, 1, ID2SYM(mid));
@@ -425,7 +461,7 @@ rb_export_method(VALUE klass, ID name, ID noex)
 	me = search_method(rb_cObject, name);
     }
 
-    if (!me || me->type == VM_METHOD_TYPE_UNDEF) {
+    if (UNDEFINED_METHOD_ENTRY_P(me)) {
 	rb_print_undef(klass, name, 0);
     }
 
@@ -450,7 +486,7 @@ rb_method_boundp(VALUE klass, ID id, int ex)
 	if (ex && (me->flag & NOEX_PRIVATE)) {
 	    return Qfalse;
 	}
-	if (me->type == VM_METHOD_TYPE_NOTIMPLEMENTED) {
+	if (!me->def || me->def->type == VM_METHOD_TYPE_NOTIMPLEMENTED) {
 	    return Qfalse;
 	}
 	return Qtrue;
@@ -520,7 +556,7 @@ rb_undef(VALUE klass, ID id)
 
     me = search_method(klass, id);
 
-    if (!me || me->type == VM_METHOD_TYPE_UNDEF) {
+    if (UNDEFINED_METHOD_ENTRY_P(me)) {
 	const char *s0 = " class";
 	VALUE c = klass;
 
@@ -746,63 +782,36 @@ rb_mod_protected_method_defined(VALUE mod, VALUE mid)
     return check_definition(mod, rb_to_id(mid), NOEX_PROTECTED);
 }
 
-static void *
-me_opts(const rb_method_entry_t *me)
-{
-    switch (me->type) {
-      case VM_METHOD_TYPE_ISEQ:
-	return me->body.iseq;
-      case VM_METHOD_TYPE_CFUNC:
-	return (void *)&me->body.cfunc;
-      case VM_METHOD_TYPE_ATTRSET:
-      case VM_METHOD_TYPE_IVAR:
-	return (void *)me->body.attr_id;
-      case VM_METHOD_TYPE_BMETHOD:
-	return (void *)me->body.proc;
-      case VM_METHOD_TYPE_ZSUPER:
-      case VM_METHOD_TYPE_NOTIMPLEMENTED:
-      case VM_METHOD_TYPE_UNDEF:
-	return 0;
-      case VM_METHOD_TYPE_OPTIMIZED:
-	return (void *)me->body.optimize_type;
-      default:
-	rb_bug("rb_add_method: unsupported method type (%d)\n", me->type);
-	return 0;
-    }
-}
-
-void
-rb_add_method_me(VALUE klass, ID mid, const rb_method_entry_t *me, rb_method_flag_t noex)
-{
-    rb_add_method(klass, mid, me->type, me_opts(me), noex);
-}
-
 int
 rb_method_entry_eq(const rb_method_entry_t *m1, const rb_method_entry_t *m2)
 {
-    if (m1->type != m2->type) {
+    const rb_method_definition_t *d1 = m1->def, *d2 = m2->def;
+    if (!d1) {
+	return !d2;
+    }
+    if (d1->type != d2->type) {
 	return 0;
     }
-    switch (m1->type) {
+    switch (d1->type) {
       case VM_METHOD_TYPE_ISEQ:
-	return m1->body.iseq == m2->body.iseq;
+	return d1->body.iseq == d2->body.iseq;
       case VM_METHOD_TYPE_CFUNC:
 	return
-	  m1->body.cfunc.func == m2->body.cfunc.func &&
-	  m1->body.cfunc.argc == m2->body.cfunc.argc;
+	  d1->body.cfunc.func == d2->body.cfunc.func &&
+	  d1->body.cfunc.argc == d2->body.cfunc.argc;
       case VM_METHOD_TYPE_ATTRSET:
       case VM_METHOD_TYPE_IVAR:
-	return m1->body.attr_id == m2->body.attr_id;
+	return d1->body.attr_id == d2->body.attr_id;
       case VM_METHOD_TYPE_BMETHOD:
-	return m1->body.proc == m2->body.proc;
+	return d1->body.proc == d2->body.proc;
       case VM_METHOD_TYPE_ZSUPER:
       case VM_METHOD_TYPE_NOTIMPLEMENTED:
       case VM_METHOD_TYPE_UNDEF:
 	return 1;
       case VM_METHOD_TYPE_OPTIMIZED:
-	return m1->body.optimize_type == m2->body.optimize_type;
+	return d1->body.optimize_type == d2->body.optimize_type;
       default:
-	rb_bug("rb_add_method: unsupported method type (%d)\n", m1->type);
+	rb_bug("rb_add_method: unsupported method type (%d)\n", d1->type);
 	return 0;
     }
 }
@@ -810,7 +819,7 @@ rb_method_entry_eq(const rb_method_entry_t *m1, const rb_method_entry_t *m2)
 void
 rb_alias(VALUE klass, ID name, ID def)
 {
-    rb_method_entry_t *orig_me, *me;
+    rb_method_entry_t *orig_me;
     VALUE singleton = 0;
 
     rb_frozen_class_p(klass);
@@ -820,11 +829,9 @@ rb_alias(VALUE klass, ID name, ID def)
 
     orig_me = search_method(klass, def);
 
-    if (!orig_me || orig_me->type == VM_METHOD_TYPE_UNDEF) {
-	if (TYPE(klass) == T_MODULE) {
-	    orig_me = search_method(rb_cObject, def);
-	}
-	if (!orig_me || !orig_me->type == VM_METHOD_TYPE_UNDEF) {
+    if (UNDEFINED_METHOD_ENTRY_P(orig_me)) {
+	if ((TYPE(klass) != T_MODULE) ||
+	    (orig_me = search_method(rb_cObject, def), UNDEFINED_METHOD_ENTRY_P(orig_me))) {
 	    rb_print_undef(klass, def, 0);
 	}
     }
@@ -832,9 +839,7 @@ rb_alias(VALUE klass, ID name, ID def)
 	singleton = rb_iv_get(klass, "__attached__");
     }
 
-    orig_me->alias_count++;
-    me = rb_add_method(klass, name, orig_me->type, me_opts(orig_me), orig_me->flag);
-    me->original_id = def;
+    rb_add_method_me(klass, name, orig_me, orig_me->flag);
 
     if (!ruby_running) return;
 
@@ -1098,10 +1103,10 @@ rb_mod_modfunc(int argc, VALUE *argv, VALUE module)
 	    if (me == 0) {
 		me = search_method(rb_cObject, id);
 	    }
-	    if (me == 0 || me->type == VM_METHOD_TYPE_UNDEF) {
+	    if (UNDEFINED_METHOD_ENTRY_P(me)) {
 		rb_print_undef(module, id, 0);
 	    }
-	    if (me->type != VM_METHOD_TYPE_ZSUPER) {
+	    if (me->def->type != VM_METHOD_TYPE_ZSUPER) {
 		break; /* normal case: need not to follow 'super' link */
 	    }
 	    m = RCLASS_SUPER(m);