Heavily refactored how lexical scope links are implemented; fix #3821

Instead of `irep` links, we added a `upper` link to `struct RProc`.
To make a space for the `upper` link, we moved `target_class` reference.
If a `Proc` does not have `env`, `target_class` is saved in an `union`
shared with `env` (if a `Proc` has env, you can tell it by `MRB_PROC_ENV_P()).
Otherwise `target_class` is referenced from `env->c`. We removed links
in `env` as well.

This change removes 2 members from `mrb_irep` struct, thus saving 2
words per method/proc/block. This also fixes potential memory leaks
due to the circular references caused by a link from `mrb_irep`.

14 files changed, 264 insertions, 270 deletions

diff --git a/include/mruby/irep.h b/include/mruby/irep.h
index 91ca8b54d..efd226793 100644
--- a/include/mruby/irep.h
+++ b/include/mruby/irep.h
@@ -45,9 +45,6 @@ typedef struct mrb_irep {
   struct mrb_irep_debug_info* debug_info;
 
   int ilen, plen, slen, rlen, refcnt;
-
-  struct mrb_irep *outer;       /* Refers outer scope */
-  struct RClass *target_class;
 } mrb_irep;
 
 #define MRB_ISEQ_NO_FREE 1
diff --git a/include/mruby/proc.h b/include/mruby/proc.h
index 5a6741610..24c9b0c21 100644
--- a/include/mruby/proc.h
+++ b/include/mruby/proc.h
@@ -18,17 +18,19 @@ MRB_BEGIN_DECL
 struct REnv {
   MRB_OBJECT_HEADER;
   mrb_value *stack;
-  ptrdiff_t cioff;
-  union {
-    mrb_sym mid;
-    struct mrb_context *c;
-  } cxt;
+  struct mrb_context *cxt;
+  // struct RProc *proc;
+  mrb_sym mid;
 };
 
-#define MRB_SET_ENV_STACK_LEN(e,len) (e)->flags = (unsigned int)(len)
-#define MRB_ENV_STACK_LEN(e) ((mrb_int)(e)->flags)
-#define MRB_ENV_UNSHARE_STACK(e) ((e)->cioff = -1)
-#define MRB_ENV_STACK_SHARED_P(e) ((e)->cioff >= 0)
+/* flags (21bits): 1(shared flag):10(cioff/bidx):10(stack_len) */
+#define MRB_ENV_SET_STACK_LEN(e,len) (e)->flags = (((e)->flags & ~0x3ff)|(unsigned int)(len) & 0x3ff)
+#define MRB_ENV_STACK_LEN(e) ((mrb_int)((e)->flags & 0x3ff))
+#define MRB_ENV_STACK_UNSHARED (1<<20)
+#define MRB_ENV_UNSHARE_STACK(e) (e)->flags |= MRB_ENV_STACK_UNSHARED
+#define MRB_ENV_STACK_SHARED_P(e) (((e)->flags & MRB_ENV_STACK_UNSHARED) == 0)
+#define MRB_ENV_BIDX(e) (((e)->flags >> 10) & 0x3ff)
+#define MRB_ENV_SET_BIDX(e,idx) (e)->flags = (((e)->flags & ~(0x3ff<<10))|((unsigned int)(idx) & 0x3ff)<<10)
 
 void mrb_env_unshare(mrb_state*, struct REnv*);
 
@@ -38,8 +40,11 @@ struct RProc {
     mrb_irep *irep;
     mrb_func_t func;
   } body;
-  struct RClass *target_class;
-  struct REnv *env;
+  struct RProc *upper;
+  union {
+    struct RClass *target_class;
+    struct REnv *env;
+  } e;
 };
 
 /* aspec access */
@@ -57,6 +62,22 @@ struct RProc {
 #define MRB_PROC_STRICT_P(p) (((p)->flags & MRB_PROC_STRICT) != 0)
 #define MRB_PROC_ORPHAN 512
 #define MRB_PROC_ORPHAN_P(p) (((p)->flags & MRB_PROC_ORPHAN) != 0)
+#define MRB_PROC_ENVSET 1024
+#define MRB_PROC_ENV_P(p) (((p)->flags & MRB_PROC_ENVSET) != 0)
+#define MRB_PROC_ENV(p) (MRB_PROC_ENV_P(p) ? (p)->e.env : NULL)
+#define MRB_PROC_TARGET_CLASS(p) (MRB_PROC_ENV_P(p) ? (p)->e.env->c : (p)->e.target_class )
+#define MRB_PROC_SET_TARGET_CLASS(p,tc) do {\
+  if (MRB_PROC_ENV_P(p)) {\
+    (p)->e.env->c = (tc);\
+    mrb_field_write_barrier(mrb, (struct RBasic*)(p)->e.env, (struct RBasic*)tc);\
+  }\
+  else {\
+    (p)->e.target_class = (tc);\
+    mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)tc);\
+  }\
+} while (0)
+#define MRB_PROC_SCOPE 2048
+#define MRB_PROC_SCOPE_P(p) (((p)->flags & MRB_PROC_SCOPE) != 0)
 
 #define mrb_proc_ptr(v)    ((struct RProc*)(mrb_ptr(v)))
 
diff --git a/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c b/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
index 891259a3f..3feb4270a 100644
--- a/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
+++ b/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
@@ -544,11 +544,11 @@ done:
         if (args.verbose) {
           mrb_codedump_all(mrb, proc);
         }
-        /* adjest stack length of toplevel environment */
+        /* adjust stack length of toplevel environment */
         if (mrb->c->cibase->env) {
           struct REnv *e = mrb->c->cibase->env;
-          if (MRB_ENV_STACK_LEN(e) < proc->body.irep->nlocals) {
-            MRB_SET_ENV_STACK_LEN(e, proc->body.irep->nlocals);
+          if (e && MRB_ENV_STACK_LEN(e) < proc->body.irep->nlocals) {
+            MRB_ENV_SET_STACK_LEN(e, proc->body.irep->nlocals);
           }
         }
         /* pass a proc for evaluation */
diff --git a/mrbgems/mruby-compiler/core/codegen.c b/mrbgems/mruby-compiler/core/codegen.c
index d9902a02e..da29077b0 100644
--- a/mrbgems/mruby-compiler/core/codegen.c
+++ b/mrbgems/mruby-compiler/core/codegen.c
@@ -3034,6 +3034,9 @@ mrb_generate_code(mrb_state *mrb, parser_state *p)
     mrb_irep_decref(mrb, scope->irep);
     mrb_pool_close(scope->mpool);
     proc->c = NULL;
+    if (mrb->c->cibase && mrb->c->cibase->proc == proc->upper) {
+      proc->upper = NULL;
+    }
     mrb->jmp = prev_jmp;
     return proc;
   }
diff --git a/mrbgems/mruby-compiler/core/parse.y b/mrbgems/mruby-compiler/core/parse.y
index bf9d3fe85..e5017b677 100644
--- a/mrbgems/mruby-compiler/core/parse.y
+++ b/mrbgems/mruby-compiler/core/parse.y
@@ -5825,7 +5825,7 @@ mrb_load_exec(mrb_state *mrb, struct mrb_parser_state *p, mrbc_context *c)
       c->keep_lv = TRUE;
     }
   }
-  proc->target_class = target;
+  MRB_PROC_SET_TARGET_CLASS(proc, target);
   if (mrb->c->ci) {
     mrb->c->ci->target_class = target;
   }
diff --git a/mrbgems/mruby-eval/src/eval.c b/mrbgems/mruby-eval/src/eval.c
index 7fd4f1437..7061565ea 100644
--- a/mrbgems/mruby-eval/src/eval.c
+++ b/mrbgems/mruby-eval/src/eval.c
@@ -13,11 +13,9 @@ static struct mrb_irep *
 get_closure_irep(mrb_state *mrb, int level)
 {
   struct mrb_context *c = mrb->c;
-  struct REnv *e = c->ci[-1].proc->env;
-  struct RProc *proc;
+  struct RProc *proc = c->ci[-1].proc;
 
   if (level == 0) {
-    proc = c->ci[-1].proc;
     if (MRB_PROC_CFUNC_P(proc)) {
       return NULL;
     }
@@ -25,16 +23,11 @@ get_closure_irep(mrb_state *mrb, int level)
   }
 
   while (--level) {
-    e = (struct REnv*)e->c;
-    if (!e) return NULL;
+    proc = proc->upper;
+    if (!proc) return NULL;
   }
 
-  if (!e) return NULL;
-  if (!MRB_ENV_STACK_SHARED_P(e)) return NULL;
-  c = e->cxt.c;
-  proc = c->cibase[e->cioff].proc;
-
-  if (!proc || MRB_PROC_CFUNC_P(proc)) {
+  if (MRB_PROC_CFUNC_P(proc)) {
     return NULL;
   }
   return proc->body.irep;
@@ -204,7 +197,9 @@ create_proc_from_string(mrb_state *mrb, char *s, mrb_int len, mrb_value binding,
   struct mrb_parser_state *p;
   struct RProc *proc;
   struct REnv *e;
-  struct mrb_context *c = mrb->c;
+  mrb_callinfo *ci = mrb->c->ci;
+  struct RClass *target_class = NULL;
+  int bidx;
 
   if (!mrb_nil_p(binding)) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "Binding of eval must be nil.");
@@ -251,19 +246,19 @@ create_proc_from_string(mrb_state *mrb, char *s, mrb_int len, mrb_value binding,
     mrbc_context_free(mrb, cxt);
     mrb_raise(mrb, E_SCRIPT_ERROR, "codegen error");
   }
-  if (c->ci[-1].proc->target_class) {
-    proc->target_class = c->ci[-1].proc->target_class;
-  }
-  e = c->ci[-1].proc->env;
-  if (!e) e = c->ci[-1].env;
-  e = (struct REnv*)mrb_obj_alloc(mrb, MRB_TT_ENV, (struct RClass*)e);
-  e->cxt.c = c;
-  e->cioff = c->ci - c->cibase;
-  e->stack = c->ci->stackent;
-  MRB_SET_ENV_STACK_LEN(e, c->ci->proc->body.irep->nlocals);
-  c->ci->target_class = proc->target_class;
-  c->ci->env = 0;
-  proc->env = e;
+  target_class = MRB_PROC_TARGET_CLASS(ci[-1].proc);
+  e = (struct REnv*)mrb_obj_alloc(mrb, MRB_TT_ENV,
+                                  (struct RClass*)target_class);
+  e->mid = ci->mid;
+  e->stack = ci->stackent;
+  MRB_ENV_SET_STACK_LEN(e, ci->proc->body.irep->nlocals);
+  bidx = ci->argc;
+  if (ci->argc < 0) bidx = 2;
+  else bidx += 1;
+  MRB_ENV_SET_BIDX(e, bidx);
+  proc->e.env = e;
+  proc->flags |= MRB_PROC_ENVSET;
+  ci->target_class = target_class;
   patch_irep(mrb, proc->body.irep, 0, proc->body.irep);
   /* mrb_codedump_all(mrb, proc); */
 
@@ -322,8 +317,7 @@ f_instance_eval(mrb_state *mrb, mrb_value self)
     mrb_get_args(mrb, "s|zi", &s, &len, &file, &line);
     cv = mrb_singleton_class(mrb, self);
     proc = create_proc_from_string(mrb, s, len, mrb_nil_value(), file, line);
-    proc->target_class = mrb_class_ptr(cv);
-    mrb->c->ci->env = NULL;
+    MRB_PROC_SET_TARGET_CLASS(proc, mrb_class_ptr(cv));
     mrb_assert(!MRB_PROC_CFUNC_P(proc));
     return exec_irep(mrb, self, proc);
   }
diff --git a/mrbgems/mruby-fiber/src/fiber.c b/mrbgems/mruby-fiber/src/fiber.c
index 57fe9401c..be9033063 100644
--- a/mrbgems/mruby-fiber/src/fiber.c
+++ b/mrbgems/mruby-fiber/src/fiber.c
@@ -123,7 +123,7 @@ fiber_init(mrb_state *mrb, mrb_value self)
 
   /* adjust return callinfo */
   ci = c->ci;
-  ci->target_class = p->target_class;
+  ci->target_class = MRB_PROC_TARGET_CLASS(p);
   ci->proc = p;
   mrb_field_write_barrier(mrb, (struct RBasic*)mrb_obj_ptr(self), (struct RBasic*)p);
   ci->pc = p->body.irep->iseq;
@@ -213,7 +213,7 @@ fiber_switch(mrb_state *mrb, mrb_value self, mrb_int len, const mrb_value *a, mr
       *b++ = *a++;
     }
     c->cibase->argc = (int)len;
-    value = c->stack[0] = c->ci->proc->env->stack[0];
+    value = c->stack[0] = MRB_PROC_ENV(c->ci->proc)->stack[0];
   }
   else {
     value = fiber_result(mrb, a, len);
diff --git a/src/class.c b/src/class.c
index a35eb4c92..77a7050da 100644
--- a/src/class.c
+++ b/src/class.c
@@ -436,8 +436,11 @@ mrb_define_method_raw(mrb_state *mrb, struct RClass *c, mrb_sym mid, struct RPro
   k = kh_put(mt, mrb, h, mid);
   kh_value(h, k) = p;
   if (p) {
+    p->flags |= MRB_PROC_SCOPE;
     p->c = NULL;
-    mrb_field_write_barrier(mrb, (struct RBasic *)c, (struct RBasic *)p);
+    mrb_field_write_barrier(mrb, (struct RBasic*)c, (struct RBasic*)p);
+    MRB_PROC_SET_TARGET_CLASS(p, c);
+    mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)c);
   }
   mc_clear_by_id(mrb, c, mid);
 }
@@ -449,7 +452,7 @@ mrb_define_method_id(mrb_state *mrb, struct RClass *c, mrb_sym mid, mrb_func_t f
   int ai = mrb_gc_arena_save(mrb);
 
   p = mrb_proc_new_cfunc(mrb, func);
-  p->target_class = c;
+  MRB_PROC_SET_TARGET_CLASS(p, c);
   mrb_define_method_raw(mrb, c, mid, p);
   mrb_gc_arena_restore(mrb, ai);
 }
diff --git a/src/gc.c b/src/gc.c
index 0f95d25ef..a3a638ae3 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -647,11 +647,8 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
     {
       struct RProc *p = (struct RProc*)obj;
 
-      mrb_gc_mark(mrb, (struct RBasic*)p->env);
-      mrb_gc_mark(mrb, (struct RBasic*)p->target_class);
-      if (!MRB_PROC_CFUNC_P(p) && p->body.irep) {
-        mrb_gc_mark(mrb, (struct RBasic*)p->body.irep->target_class);
-      }
+      mrb_gc_mark(mrb, (struct RBasic*)p->upper);
+      mrb_gc_mark(mrb, (struct RBasic*)p->e.env);
     }
     break;
 
@@ -660,12 +657,6 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
       struct REnv *e = (struct REnv*)obj;
       mrb_int i, len;
 
-      if (MRB_ENV_STACK_SHARED_P(e)) {
-        if (e->cxt.c->fib) {
-          mrb_gc_mark(mrb, (struct RBasic*)e->cxt.c->fib);
-        }
-        break;
-      }
       len = MRB_ENV_STACK_LEN(e);
       for (i=0; i<len; i++) {
         mrb_gc_mark_value(mrb, e->stack[i]);
diff --git a/src/kernel.c b/src/kernel.c
index 33d142184..1e5a74222 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -136,6 +136,7 @@ mrb_f_block_given_p_m(mrb_state *mrb, mrb_value self)
 {
   mrb_callinfo *ci = mrb->c->ci;
   mrb_value *bp;
+  struct RProc *p;
 
   bp = ci->stackent + 1;
   ci--;
@@ -143,24 +144,20 @@ mrb_f_block_given_p_m(mrb_state *mrb, mrb_value self)
     return mrb_false_value();
   }
   /* block_given? called within block; check upper scope */
-  if (ci->proc->env) {
-    struct REnv *e = ci->proc->env;
-
-    while (e->c) {
-      e = (struct REnv*)e->c;
-    }
+  p = ci->proc;
+  while (p) {
+    if (MRB_PROC_SCOPE_P(p)) break;
+    p = p->upper;
+  }
+  /* top-level does not have block slot (always false) */
+  if (p == NULL) return mrb_false_value();
+  if (MRB_PROC_ENV_P(p)) {
+    struct REnv *e = MRB_PROC_ENV(p);
     /* top-level does not have block slot (always false) */
     if (e->stack == mrb->c->stbase)
       return mrb_false_value();
-    if (e->stack && e->cioff < 0) {
-      /* use saved block arg position */
-      bp = &e->stack[-e->cioff];
-      ci = 0;                 /* no callinfo available */
-    }
-    else {
-      ci = e->cxt.c->cibase + e->cioff;
-      bp = ci[1].stackent + 1;
-    }
+    /* use saved block arg position */
+    bp = &e->stack[MRB_ENV_BIDX(e)];
   }
   if (ci && ci->argc > 0) {
     bp += ci->argc;
@@ -655,7 +652,7 @@ method_entry_loop(mrb_state *mrb, struct RClass* klass, khash_t(st)* set)
   khint_t i;
 
   khash_t(mt) *h = klass->mt;
-  if (!h) return;
+  if (!h || kh_size(h) == 0) return;
   for (i=0;i<kh_end(h);i++) {
     if (kh_exist(h, i) && kh_value(h, i)) {
       kh_put(st, mrb, set, kh_key(h, i));
@@ -690,7 +687,7 @@ mrb_class_instance_method_list(mrb_state *mrb, mrb_bool recur, struct RClass* kl
     klass = klass->super;
   }
 
-  ary = mrb_ary_new(mrb);
+  ary = mrb_ary_new_capa(mrb, kh_size(set));
   for (i=0;i<kh_end(set);i++) {
     if (kh_exist(set, i)) {
       mrb_ary_push(mrb, ary, mrb_symbol_value(kh_key(set, i)));
@@ -1161,16 +1158,19 @@ mrb_local_variables(mrb_state *mrb, mrb_value self)
     return mrb_ary_new(mrb);
   }
   vars = mrb_hash_new(mrb);
-  irep = proc->body.irep;
-  while (irep) {
+  while (proc) {
+    if (MRB_PROC_CFUNC_P(proc)) break;
+    irep = proc->body.irep;
     if (!irep->lv) break;
     for (i = 0; i + 1 < irep->nlocals; ++i) {
       if (irep->lv[i].name) {
         mrb_hash_set(mrb, vars, mrb_symbol_value(irep->lv[i].name), mrb_true_value());
       }
     }
-    if (!proc->env) break;
-    irep = irep->outer;
+    if (!MRB_PROC_ENV_P(proc)) break;
+    proc = proc->upper;
+    // if (MRB_PROC_SCOPE_P(proc)) break;
+    if (!proc->c) break;
   }
 
   return mrb_hash_keys(mrb, vars);
diff --git a/src/proc.c b/src/proc.c
index a6214f1fc..69a9c0299 100644
--- a/src/proc.c
+++ b/src/proc.c
@@ -20,15 +20,19 @@ mrb_proc_new(mrb_state *mrb, mrb_irep *irep)
   mrb_callinfo *ci = mrb->c->ci;
 
   p = (struct RProc*)mrb_obj_alloc(mrb, MRB_TT_PROC, mrb->proc_class);
-  p->target_class = 0;
   if (ci) {
-    if (ci->proc)
-      p->target_class = ci->proc->target_class;
-    if (!p->target_class)
-      p->target_class = ci->target_class;
+    struct RClass *tc = NULL;
+
+    if (ci->proc) {
+      tc = MRB_PROC_TARGET_CLASS(ci->proc);
+    }
+    if (tc == NULL) {
+      tc = ci->target_class;
+    }
+    p->upper = ci->proc;
+    p->e.target_class = tc;
   }
   p->body.irep = irep;
-  p->env = 0;
   mrb_irep_incref(mrb, irep);
 
   return p;
@@ -38,30 +42,45 @@ static struct REnv*
 env_new(mrb_state *mrb, mrb_int nlocals)
 {
   struct REnv *e;
-
-  e = (struct REnv*)mrb_obj_alloc(mrb, MRB_TT_ENV, (struct RClass*)mrb->c->ci->proc->env);
-  MRB_SET_ENV_STACK_LEN(e, nlocals);
-  e->cxt.c = mrb->c;
-  e->cioff = mrb->c->ci - mrb->c->cibase;
+  mrb_callinfo *ci = mrb->c->ci;
+  int bidx;
+
+  e = (struct REnv*)mrb_obj_alloc(mrb, MRB_TT_ENV, NULL);
+  MRB_ENV_SET_STACK_LEN(e, nlocals);
+  bidx = ci->argc;
+  if (ci->argc < 0) bidx = 2;
+  else bidx += 1;
+  MRB_ENV_SET_BIDX(e, bidx);
+  e->mid = ci->mid;
   e->stack = mrb->c->stack;
+  e->cxt = mrb->c;
 
   return e;
 }
 
 static void
-closure_setup(mrb_state *mrb, struct RProc *p, int nlocals)
+closure_setup(mrb_state *mrb, struct RProc *p)
 {
+  mrb_callinfo *ci = mrb->c->ci;
+  struct RProc *up = p->upper;
   struct REnv *e;
 
-  if (!mrb->c->ci->env) {
-    e = env_new(mrb, nlocals);
-    mrb->c->ci->env = e;
+  if (ci->env) {
+    e = ci->env;
   }
   else {
-    e = mrb->c->ci->env;
+    struct RClass *tc = MRB_PROC_TARGET_CLASS(up);
+
+    e = env_new(mrb, up->body.irep->nlocals);
+    ci->env = e;
+    if (tc) {
+      e->c = tc;
+      mrb_field_write_barrier(mrb, (struct RBasic*)e, (struct RBasic*)tc);
+    }
   }
-  p->env = e;
-  mrb_field_write_barrier(mrb, (struct RBasic *)p, (struct RBasic *)p->env);
+  p->e.env = e;
+  p->flags |= MRB_PROC_ENVSET;
+  mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)e);
 }
 
 struct RProc*
@@ -69,7 +88,7 @@ mrb_closure_new(mrb_state *mrb, mrb_irep *irep)
 {
   struct RProc *p = mrb_proc_new(mrb, irep);
 
-  closure_setup(mrb, p, mrb->c->ci->proc->body.irep->nlocals);
+  closure_setup(mrb, p);
   return p;
 }
 
@@ -81,7 +100,8 @@ mrb_proc_new_cfunc(mrb_state *mrb, mrb_func_t func)
   p = (struct RProc*)mrb_obj_alloc(mrb, MRB_TT_PROC, mrb->proc_class);
   p->body.func = func;
   p->flags |= MRB_PROC_CFUNC;
-  p->env = 0;
+  p->upper = 0;
+  p->e.target_class = 0;
 
   return p;
 }
@@ -93,8 +113,9 @@ mrb_proc_new_cfunc_with_env(mrb_state *mrb, mrb_func_t func, mrb_int argc, const
   struct REnv *e;
   int i;
 
-  p->env = e = env_new(mrb, argc);
-  mrb_field_write_barrier(mrb, (struct RBasic *)p, (struct RBasic *)p->env);
+  p->e.env = e = env_new(mrb, argc);
+  p->flags |= MRB_PROC_ENVSET;
+  mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)e);
   MRB_ENV_UNSHARE_STACK(e);
   e->stack = (mrb_value*)mrb_malloc(mrb, sizeof(mrb_value) * argc);
   if (argv) {
@@ -120,7 +141,7 @@ MRB_API mrb_value
 mrb_proc_cfunc_env_get(mrb_state *mrb, mrb_int idx)
 {
   struct RProc *p = mrb->c->ci->proc;
-  struct REnv *e = p->env;
+  struct REnv *e = MRB_PROC_ENV(p);
 
   if (!MRB_PROC_CFUNC_P(p)) {
     mrb_raise(mrb, E_TYPE_ERROR, "Can't get cfunc env from non-cfunc proc.");
@@ -148,8 +169,9 @@ mrb_proc_copy(struct RProc *a, struct RProc *b)
   if (!MRB_PROC_CFUNC_P(a) && a->body.irep) {
     a->body.irep->refcnt++;
   }
-  a->target_class = b->target_class;
-  a->env = b->env;
+  a->upper = b->upper;
+  a->e.env = b->e.env;
+  /* a->e.target_class = a->e.target_class; */
 }
 
 static mrb_value
@@ -169,7 +191,7 @@ mrb_proc_s_new(mrb_state *mrb, mrb_value proc_class)
   proc = mrb_obj_value(p);
   mrb_funcall_with_block(mrb, proc, mrb_intern_lit(mrb, "initialize"), 0, NULL, proc);
   if (!MRB_PROC_STRICT_P(p) &&
-      mrb->c->ci > mrb->c->cibase && p->env == mrb->c->ci[-1].env) {
+      mrb->c->ci > mrb->c->cibase && MRB_PROC_ENV(p) == mrb->c->ci[-1].env) {
     p->flags |= MRB_PROC_ORPHAN;
   }
   return proc;
diff --git a/src/state.c b/src/state.c
index 596eecafa..44bcc0656 100644
--- a/src/state.c
+++ b/src/state.c
@@ -139,11 +139,6 @@ mrb_irep_cutref(mrb_state *mrb, mrb_irep *irep)
     irep->reps[i] = NULL;
     if (tmp) mrb_irep_decref(mrb, tmp);
   }
-  if (irep->outer) {
-    tmp = irep->outer;
-    irep->outer = NULL;
-    if (tmp) mrb_irep_decref(mrb, tmp);
-  }
 }
 
 void
@@ -170,10 +165,6 @@ mrb_irep_free(mrb_state *mrb, mrb_irep *irep)
     if (irep->reps[i])
       mrb_irep_decref(mrb, irep->reps[i]);
   }
-  if (irep->outer) {
-    if (irep->outer)
-      mrb_irep_decref(mrb, irep->outer);
-  }
   mrb_free(mrb, irep->reps);
   mrb_free(mrb, irep->lv);
   if (irep->own_filename) {
diff --git a/src/variable.c b/src/variable.c
index 4fbe82dd9..3e84c573c 100644
--- a/src/variable.c
+++ b/src/variable.c
@@ -632,18 +632,19 @@ mrb_cv_defined(mrb_state *mrb, mrb_value mod, mrb_sym sym)
 mrb_value
 mrb_vm_cv_get(mrb_state *mrb, mrb_sym sym)
 {
-  struct RClass *c = mrb->c->ci->proc->target_class;
+  struct RClass *c;
 
+  c = MRB_PROC_TARGET_CLASS(mrb->c->ci->proc);
   if (!c) c = mrb->c->ci->target_class;
-
   return mrb_mod_cv_get(mrb, c, sym);
 }
 
 void
 mrb_vm_cv_set(mrb_state *mrb, mrb_sym sym, mrb_value v)
 {
-  struct RClass *c = mrb->c->ci->proc->target_class;
+  struct RClass *c;
 
+  c = MRB_PROC_TARGET_CLASS(mrb->c->ci->proc);
   if (!c) c = mrb->c->ci->target_class;
   mrb_mod_cv_set(mrb, c, sym, v);
 }
@@ -700,11 +701,12 @@ mrb_const_get(mrb_state *mrb, mrb_value mod, mrb_sym sym)
 mrb_value
 mrb_vm_const_get(mrb_state *mrb, mrb_sym sym)
 {
-  struct RClass *c = mrb->c->ci->proc->target_class;
+  struct RClass *c;
   struct RClass *c2;
   mrb_value v;
-  mrb_irep *irep;
+  struct RProc *proc;
 
+  c = MRB_PROC_TARGET_CLASS(mrb->c->ci->proc);
   if (!c) c = mrb->c->ci->target_class;
   mrb_assert(c != NULL);
 
@@ -720,15 +722,13 @@ mrb_vm_const_get(mrb_state *mrb, mrb_sym sym)
   }
   if (c2->tt == MRB_TT_CLASS || c2->tt == MRB_TT_MODULE) c = c2;
   mrb_assert(!MRB_PROC_CFUNC_P(mrb->c->ci->proc));
-  irep = mrb->c->ci->proc->body.irep;
-  while (irep) {
-    if (irep->target_class) {
-      c2 = irep->target_class;
-      if (c2->iv && iv_get(mrb, c2->iv, sym, &v)) {
-        return v;
-      }
+  proc = mrb->c->ci->proc;
+  while (proc) {
+    c2 = MRB_PROC_TARGET_CLASS(proc);
+    if (c2 && c2->iv && iv_get(mrb, c2->iv, sym, &v)) { 
+      return v;
     }
-    irep = irep->outer;
+    proc = proc->upper;
   }
   return const_get(mrb, c, sym, TRUE);
 }
@@ -746,9 +746,7 @@ mrb_const_set(mrb_state *mrb, mrb_value mod, mrb_sym sym, mrb_value v)
 void
 mrb_vm_const_set(mrb_state *mrb, mrb_sym sym, mrb_value v)
 {
-  struct RClass *c = mrb->c->ci->proc->target_class;
-
-  if (!c) c = mrb->c->ci->target_class;
+  struct RClass *c = mrb->c->ci->target_class;
   mrb_obj_iv_set(mrb, (struct RObject*)c, sym, v);
 }
 
diff --git a/src/vm.c b/src/vm.c
index 196b2934e..734d225ba 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -151,6 +151,9 @@ envadjust(mrb_state *mrb, mrb_value *oldbase, mrb_value *newbase, size_t size)
 
       e->stack = newbase + off;
     }
+    else if (e && MRB_ENV_STACK_SHARED_P(e)) {
+      fprintf(stderr, "bingo! %p\n", e);
+    }
     ci->stackent = newbase + (ci->stackent - oldbase);
     ci++;
   }
@@ -208,41 +211,33 @@ stack_extend(mrb_state *mrb, int room)
   }
 }
 
+static int nenv = 0;
+
 static inline struct REnv*
 uvenv(mrb_state *mrb, int up)
 {
-  struct REnv *e = mrb->c->ci->proc->env;
+  struct RProc *proc = mrb->c->ci->proc;
+  struct REnv *e;
 
-  while (up--) {
+  nenv++;
+  do {
+    e = MRB_PROC_ENV(proc);
     if (!e) return NULL;
-    e = (struct REnv*)e->c;
-  }
+    proc = proc->upper;
+    if (!proc) return NULL;
+  } while (up--);
   return e;
 }
 
-static inline mrb_bool
-is_strict(mrb_state *mrb, struct REnv *e)
+static inline struct RProc*
+top_proc(mrb_state *mrb, struct RProc *proc)
 {
-  ptrdiff_t cioff = e->cioff;
-
-  if (MRB_ENV_STACK_SHARED_P(e) && e->cxt.c->cibase[cioff].proc &&
-      MRB_PROC_STRICT_P(e->cxt.c->cibase[cioff].proc)) {
-    return TRUE;
+  while (proc->upper) {
+    if (MRB_PROC_SCOPE_P(proc) || MRB_PROC_STRICT_P(proc))
+      return proc;
+    proc = proc->upper;
   }
-  return FALSE;
-}
-
-static inline struct REnv*
-top_env(mrb_state *mrb, struct RProc *proc)
-{
-  struct REnv *e = proc->env;
-
-  if (is_strict(mrb, e)) return e;
-  while (e->c) {
-    e = (struct REnv*)e->c;
-    if (is_strict(mrb, e)) return e;
-  }
-  return e;
+  return proc;
 }
 
 #define CI_ACC_SKIP    -1
@@ -279,19 +274,11 @@ mrb_env_unshare(mrb_state *mrb, struct REnv *e)
   if (e == NULL) return;
   else {
     size_t len = (size_t)MRB_ENV_STACK_LEN(e);
-    ptrdiff_t cioff = e->cioff;
     mrb_value *p;
 
     if (!MRB_ENV_STACK_SHARED_P(e)) return;
-    if (e->cxt.c != mrb->c) return;
-    if (e->cioff == 0 && e->cxt.c == mrb->root_c) return;
+    if (e->cxt != mrb->c) return;
     MRB_ENV_UNSHARE_STACK(e);
-    if (!e->c) {
-      /* save block argument position (negated) */
-      e->cioff = -e->cxt.c->cibase[cioff].argc-1;
-      if (e->cioff == 0) e->cioff = -2; /* blkarg position for vararg (1:args, 2:blk) */
-    }
-    e->cxt.mid = e->cxt.c->cibase[cioff].mid;
     p = (mrb_value *)mrb_malloc(mrb, sizeof(mrb_value)*len);
     if (len > 0) {
       stack_copy(p, e->stack, len);
@@ -317,20 +304,22 @@ static void
 ecall(mrb_state *mrb, int i)
 {
   struct RProc *p;
-  mrb_callinfo *ci = mrb->c->ci;
-  mrb_value *self = mrb->c->stack;
+  struct mrb_context *c = mrb->c;
+  mrb_callinfo *ci = c->ci;
   struct RObject *exc;
+  struct REnv *env;
   ptrdiff_t cioff;
   int ai = mrb_gc_arena_save(mrb);
 
   if (i<0) return;
-  if (ci - mrb->c->cibase > MRB_FUNCALL_DEPTH_MAX) {
+  if (ci - c->cibase > MRB_FUNCALL_DEPTH_MAX) {
     mrb_exc_raise(mrb, mrb_obj_value(mrb->stack_err));
   }
-  p = mrb->c->ensure[i];
+  p = c->ensure[i];
   if (!p) return;
-  mrb->c->ensure[i] = NULL;
-  cioff = ci - mrb->c->cibase;
+  mrb_assert(!MRB_PROC_CFUNC_P(p));
+  c->ensure[i] = NULL;
+  cioff = ci - c->cibase;
   ci = cipush(mrb);
   ci->stackent = mrb->c->stack;
   ci->mid = ci[-1].mid;
@@ -338,14 +327,17 @@ ecall(mrb_state *mrb, int i)
   ci->argc = 0;
   ci->proc = p;
   ci->nregs = p->body.irep->nregs;
-  ci->target_class = p->target_class;
-  mrb->c->stack = mrb->c->stack + ci[-1].nregs;
+  ci->target_class = MRB_PROC_TARGET_CLASS(p);
+  env = MRB_PROC_ENV(p);
+  mrb_assert(env);
+  c->stack = c->stack + p->body.irep->nregs;
   exc = mrb->exc; mrb->exc = 0;
   if (exc) {
     mrb_gc_protect(mrb, mrb_obj_value(exc));
   }
-  mrb_run(mrb, p, *self);
-  mrb->c->ci = mrb->c->cibase + cioff;
+  mrb_run(mrb, p, env->stack[0]);
+  c = mrb->c;
+  c->ci = c->cibase + cioff;
   if (!mrb->exc) mrb->exc = exc;
   mrb_gc_arena_restore(mrb, ai);
 }
@@ -497,7 +489,7 @@ mrb_exec_irep(mrb_state *mrb, mrb_value self, struct RProc *p)
 
   mrb->c->stack[0] = self;
   ci->proc = p;
-  ci->target_class = p->target_class;
+  ci->target_class = MRB_PROC_TARGET_CLASS(p);
   if (MRB_PROC_CFUNC_P(p)) {
     return p->body.func(mrb, self);
   }
@@ -732,7 +724,7 @@ mrb_yield_argv(mrb_state *mrb, mrb_value b, mrb_int argc, const mrb_value *argv)
 {
   struct RProc *p = mrb_proc_ptr(b);
 
-  return mrb_yield_with_class(mrb, b, argc, argv, p->env->stack[0], p->target_class);
+  return mrb_yield_with_class(mrb, b, argc, argv, MRB_PROC_ENV(p)->stack[0], MRB_PROC_TARGET_CLASS(p));
 }
 
 MRB_API mrb_value
@@ -740,7 +732,7 @@ mrb_yield(mrb_state *mrb, mrb_value b, mrb_value arg)
 {
   struct RProc *p = mrb_proc_ptr(b);
 
-  return mrb_yield_with_class(mrb, b, 1, &arg, p->env->stack[0], p->target_class);
+  return mrb_yield_with_class(mrb, b, 1, &arg, MRB_PROC_ENV(p)->stack[0], MRB_PROC_TARGET_CLASS(p));
 }
 
 mrb_value
@@ -770,23 +762,23 @@ mrb_value
 mrb_mod_s_nesting(mrb_state *mrb, mrb_value mod)
 {
   struct RProc *proc;
-  mrb_irep *irep;
   mrb_value ary;
-  struct RClass *c;
+  struct RClass *c = NULL;
 
   mrb_get_args(mrb, "");
   ary = mrb_ary_new(mrb);
   proc = mrb->c->ci[-1].proc;   /* callee proc */
-  c = proc->target_class;
-  mrb_ary_push(mrb, ary, mrb_obj_value(c));
   mrb_assert(!MRB_PROC_CFUNC_P(proc));
-  irep = proc->body.irep;
-  while (irep) {
-    if (irep->target_class && irep->target_class != c) {
-      c = irep->target_class;
-      mrb_ary_push(mrb, ary, mrb_obj_value(c));
+  while (proc) {
+    if (MRB_PROC_SCOPE_P(proc)) {
+      struct RClass *c2 = MRB_PROC_TARGET_CLASS(proc);
+
+      if (c2 != c) {
+        c = c2;
+        mrb_ary_push(mrb, ary, mrb_obj_value(c));
+      }
     }
-    irep = irep->outer;
+    proc = proc->upper;
   }
   return ary;
 }
@@ -852,18 +844,6 @@ argnum_error(mrb_state *mrb, mrb_int num)
   mrb_exc_set(mrb, exc);
 }
 
-void
-irep_uplink(mrb_state *mrb, mrb_irep *outer, mrb_irep *irep)
-{
-  if (irep->outer != outer) {
-    if (irep->outer) {
-      mrb_irep_decref(mrb, irep->outer);
-    }
-    irep->outer = outer;
-    mrb_irep_incref(mrb, outer);
-  }
-}
-
 #define ERR_PC_SET(mrb, pc) mrb->c->ci->err = pc;
 #define ERR_PC_CLR(mrb)     mrb->c->ci->err = 0;
 #ifdef MRB_ENABLE_DEBUG_HOOK
@@ -1319,9 +1299,10 @@ RETRY_TRY_BLOCK:
     CASE(OP_EPOP) {
       /* A      A.times{ensure_pop().call} */
       int a = GETARG_A(i);
-      int n, epos = mrb->c->ci->epos;
-      mrb_callinfo *ci;
+      mrb_callinfo *ci = mrb->c->ci;
+      int n, epos = ci->epos;
       mrb_value self = regs[0];
+      struct RClass *target_class = ci->target_class;
 
       if (mrb->c->eidx == epos) {
         NEXT;
@@ -1339,7 +1320,7 @@ RETRY_TRY_BLOCK:
         ci->proc = proc;
         ci->stackent = mrb->c->stack;
         ci->nregs = irep->nregs;
-        ci->target_class = proc->target_class;
+        ci->target_class = target_class;
         ci->pc = pc;
         ci->acc = ci[-1].nregs;
         mrb->c->stack += ci->acc;
@@ -1441,7 +1422,7 @@ RETRY_TRY_BLOCK:
         if (GET_OPCODE(i) == OP_SENDB) {
           if (mrb_type(blk) == MRB_TT_PROC) {
             struct RProc *p = mrb_proc_ptr(blk);
-            if (p && !MRB_PROC_STRICT_P(p) && p->env == ci[-1].env) {
+            if (p && !MRB_PROC_STRICT_P(p) && MRB_PROC_ENV(p) == ci[-1].env) {
               p->flags |= MRB_PROC_ORPHAN;
             }
           }
@@ -1493,20 +1474,16 @@ RETRY_TRY_BLOCK:
 
       /* replace callinfo */
       ci = mrb->c->ci;
-      ci->target_class = m->target_class;
+      ci->target_class = MRB_PROC_TARGET_CLASS(m);
       ci->proc = m;
-      if (m->env) {
+      if (MRB_PROC_ENV_P(m)) {
         mrb_sym mid;
+        struct REnv *e = MRB_PROC_ENV(m);
 
-        if (MRB_ENV_STACK_SHARED_P(m->env)) {
-          mid = m->env->cxt.c->cibase[m->env->cioff].mid;
-        }
-        else {
-          mid = m->env->cxt.mid;
-        }
+        mid = e->mid;
         if (mid) ci->mid = mid;
-        if (!m->env->stack) {
-          m->env->stack = mrb->c->stack;
+        if (!e->stack) {
+          e->stack = mrb->c->stack;
         }
       }
 
@@ -1547,8 +1524,8 @@ RETRY_TRY_BLOCK:
         else if (ci->argc+2 < irep->nregs) {
           stack_clear(regs+ci->argc+2, irep->nregs-ci->argc-2);
         }
-        if (m->env) {
-          regs[0] = m->env->stack[0];
+        if (MRB_PROC_ENV_P(m)) {
+          regs[0] = MRB_PROC_ENV(m)->stack[0];
         }
         pc = irep->iseq;
         JUMP;
@@ -1833,6 +1810,12 @@ RETRY_TRY_BLOCK:
       /* A B     return R(A) (B=normal,in-block return/break) */
       mrb_callinfo *ci;
 
+#define ecall_adjust() do {\
+  ptrdiff_t cioff = ci - mrb->c->cibase;\
+  ecall(mrb, --mrb->c->eidx);\
+  ci = mrb->c->cibase + cioff;\
+} while (0)
+
       ci = mrb->c->ci;
       if (ci->mid) {
         mrb_value blk;
@@ -1847,18 +1830,17 @@ RETRY_TRY_BLOCK:
           struct RProc *p = mrb_proc_ptr(blk);
 
           if (!MRB_PROC_STRICT_P(p) &&
-              ci > mrb->c->cibase && p->env == ci[-1].env) {
+              ci > mrb->c->cibase && MRB_PROC_ENV(p) == ci[-1].env) {
             p->flags |= MRB_PROC_ORPHAN;
           }
         }
       }
 
       if (mrb->exc) {
-        mrb_callinfo *ci0;
         mrb_value *stk;
 
       L_RAISE:
-        ci0 = ci = mrb->c->ci;
+        ci = mrb->c->ci;
         if (ci == mrb->c->cibase) {
           if (ci->ridx == 0) goto L_FTOP;
           goto L_RESCUE;
@@ -1897,8 +1879,7 @@ RETRY_TRY_BLOCK:
           if (ci[0].ridx == ci[-1].ridx) {
             mrb_value *org_stbase = mrb->c->stbase;
             while (mrb->c->eidx > ci->epos) {
-              ecall(mrb, --mrb->c->eidx);
-              ci = mrb->c->ci;
+              ecall_adjust();
               if (org_stbase != mrb->c->stbase) {
                 stk = mrb->c->stack;
               }
@@ -1911,46 +1892,43 @@ RETRY_TRY_BLOCK:
         irep = proc->body.irep;
         pool = irep->pool;
         syms = irep->syms;
-        if (ci != ci0) {
-          mrb->c->stack = ci[1].stackent;
-        }
+        mrb->c->stack = ci[1].stackent;
         stack_extend(mrb, irep->nregs);
         pc = mrb->c->rescue[--ci->ridx];
       }
       else {
         int acc;
         mrb_value v;
+        struct RProc *dst;
 
+        ci = mrb->c->ci;
         v = regs[GETARG_A(i)];
         mrb_gc_protect(mrb, v);
         switch (GETARG_B(i)) {
         case OP_R_RETURN:
           /* Fall through to OP_R_NORMAL otherwise */
-          if (ci->acc >=0 && proc->env && !MRB_PROC_STRICT_P(proc)) {
-            struct REnv *e = top_env(mrb, proc);
-            mrb_callinfo *ce;
+          if (ci->acc >=0 && MRB_PROC_ENV_P(proc) && !MRB_PROC_STRICT_P(proc)) {
+            dst = top_proc(mrb, proc); 
 
-            if (!MRB_ENV_STACK_SHARED_P(e) || e->cxt.c != mrb->c) {
-              localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
-              goto L_RAISE;
+            if (MRB_PROC_ENV_P(dst)) {
+              struct REnv *e = MRB_PROC_ENV(dst);
+
+              if (!MRB_ENV_STACK_SHARED_P(e) || e->cxt != mrb->c) {
+                localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
+                goto L_RAISE;
+              }
             }
-            
-            ce = mrb->c->cibase + e->cioff;
-            while (ci > ce) {
-              mrb_env_unshare(mrb, ci->env);
+            while (ci->proc != dst) {
               if (ci->acc < 0) {
                 localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
                 goto L_RAISE;
               }
               ci--;
             }
-            mrb_env_unshare(mrb, ci->env);
-            if (ce == mrb->c->cibase) {
+            if (ci == mrb->c->cibase) {
               localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
               goto L_RAISE;
             }
-            mrb->c->stack = mrb->c->ci->stackent;
-            mrb->c->ci = ce;
             break;
           }
         case OP_R_NORMAL:
@@ -1966,14 +1944,14 @@ RETRY_TRY_BLOCK:
               goto L_RAISE;
             }
             while (mrb->c->eidx > 0) {
-              ecall(mrb, --mrb->c->eidx);
+              ecall_adjust();
             }
             /* automatic yield at the end */
             mrb->c->status = MRB_FIBER_TERMINATED;
             mrb->c = mrb->c->prev;
             mrb->c->status = MRB_FIBER_RUNNING;
+            ci = mrb->c->ci;
           }
-          ci = mrb->c->ci;
           break;
         case OP_R_BREAK:
           if (MRB_PROC_STRICT_P(proc)) goto NORMAL_RETURN;
@@ -1986,23 +1964,23 @@ RETRY_TRY_BLOCK:
             mrb_exc_set(mrb, exc);
             goto L_RAISE;
           }
-          if (!proc->env || !MRB_ENV_STACK_SHARED_P(proc->env)) {
+          if (!MRB_PROC_ENV_P(proc) || !MRB_ENV_STACK_SHARED_P(MRB_PROC_ENV(proc))) {
             goto L_BREAK_ERROR;
           }
-          if (proc->env->cxt.c != mrb->c) {
+          if (MRB_PROC_ENV(proc)->cxt != mrb->c) {
             goto L_BREAK_ERROR;
           }
-          while (mrb->c->eidx > mrb->c->ci->epos) {
-            ecall(mrb, --mrb->c->eidx);
-          }
           /* break from fiber block */
-          if (mrb->c->ci == mrb->c->cibase && mrb->c->ci->pc) {
+          if (ci == mrb->c->cibase && ci->pc) {
             struct mrb_context *c = mrb->c;
 
+            while (c->eidx > c->ci->epos) {
+              ecall_adjust();
+            }
             mrb->c = c->prev;
             c->prev = NULL;
+            ci = mrb->c->ci;
           }
-          ci = mrb->c->ci;
           if (ci->acc < 0) {
             mrb_gc_arena_restore(mrb, ai);
             mrb->c->vmexec = FALSE;
@@ -2018,31 +1996,32 @@ RETRY_TRY_BLOCK:
             ci = mrb->c->ci;
           }
           mrb->c->stack = ci->stackent;
-          mrb->c->ci = mrb->c->cibase + proc->env->cioff + 1;
-          while (ci > mrb->c->ci) {
-            mrb_env_unshare(mrb, ci->env);
+          proc = proc->upper;
+          while (mrb->c->cibase < ci &&  ci[-1].proc != proc) {
             if (ci[-1].acc == CI_ACC_SKIP) {
               mrb->c->ci = ci;
               goto L_BREAK_ERROR;
             }
             ci--;
           }
-          mrb_env_unshare(mrb, ci->env);
           break;
         default:
           /* cannot happen */
           break;
         }
-        while (mrb->c->eidx > mrb->c->ci->epos) {
-          ecall(mrb, --mrb->c->eidx);
+        while (mrb->c->eidx > ci->epos) {
+          ecall_adjust();
         }
-        if (mrb->c->vmexec && !mrb->c->ci->target_class) {
+        if (mrb->c->vmexec && !ci->target_class) {
           mrb_gc_arena_restore(mrb, ai);
           mrb->c->vmexec = FALSE;
           mrb->jmp = prev_jmp;
           return v;
         }
-        ci = mrb->c->ci;
+        while (ci < mrb->c->ci) {
+          mrb_env_unshare(mrb, mrb->c->ci->env);
+          mrb->c->ci--;
+        }
         acc = ci->acc;
         mrb->c->stack = ci->stackent;
         cipop(mrb);
@@ -2052,6 +2031,7 @@ RETRY_TRY_BLOCK:
           return v;
         }
         pc = ci->pc;
+        ci = mrb->c->ci;
         DEBUG(fprintf(stderr, "from :%s\n", mrb_sym2name(mrb, ci->mid)));
         proc = mrb->c->ci->proc;
         irep = proc->body.irep;
@@ -2152,8 +2132,7 @@ RETRY_TRY_BLOCK:
       if (lv == 0) stack = regs + 1;
       else {
         struct REnv *e = uvenv(mrb, lv-1);
-        if (!e || e->cioff == 0 ||
-            (!MRB_ENV_STACK_SHARED_P(e) && e->cxt.mid == 0) ||
+        if (!e || (!MRB_ENV_STACK_SHARED_P(e) && e->mid == 0) ||
             MRB_ENV_STACK_LEN(e) <= m1+r+m2+1) {
           localjump_error(mrb, LOCALJUMP_ERROR_YIELD);
           goto L_RAISE;
@@ -2689,7 +2668,6 @@ RETRY_TRY_BLOCK:
       int c = GETARG_c(i);
       mrb_irep *nirep = irep->reps[b];
 
-      irep_uplink(mrb, irep, nirep);
       if (c & OP_L_CAPTURE) {
         p = mrb_closure_new(mrb, nirep);
       }
@@ -2718,9 +2696,7 @@ RETRY_TRY_BLOCK:
       base = regs[a];
       super = regs[a+1];
       if (mrb_nil_p(base)) {
-        baseclass = mrb->c->ci->proc->target_class;
-        if (!baseclass) baseclass = mrb->c->ci->target_class;
-
+        baseclass = mrb->c->ci->target_class;
         base = mrb_obj_value(baseclass);
       }
       c = mrb_vm_define_class(mrb, base, super, id);
@@ -2738,9 +2714,7 @@ RETRY_TRY_BLOCK:
 
       base = regs[a];
       if (mrb_nil_p(base)) {
-        baseclass = mrb->c->ci->proc->target_class;
-        if (!baseclass) baseclass = mrb->c->ci->target_class;
-
+        baseclass = mrb->c->ci->target_class;
         base = mrb_obj_value(baseclass);
       }
       c = mrb_vm_define_module(mrb, base, id);
@@ -2758,11 +2732,12 @@ RETRY_TRY_BLOCK:
       struct RProc *p;
       mrb_irep *nirep = irep->reps[bx];
 
-      irep_uplink(mrb, irep, nirep);
-      nirep->target_class = mrb_class_ptr(recv);
       /* prepare closure */
-      p = mrb_closure_new(mrb, nirep);
+      p = mrb_proc_new(mrb, nirep);
       p->c = NULL;
+      mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)proc);
+      MRB_PROC_SET_TARGET_CLASS(p, mrb_class_ptr(recv));
+      p->flags |= MRB_PROC_SCOPE;
 
       /* prepare stack */
       ci = cipush(mrb);
@@ -2777,7 +2752,7 @@ RETRY_TRY_BLOCK:
       mrb->c->stack += a;
 
       /* setup closure */
-      p->target_class = ci->target_class;
+      MRB_PROC_SET_TARGET_CLASS(p, ci->target_class);
       ci->proc = p;
 
       irep = p->body.irep;
@@ -2908,7 +2883,6 @@ mrb_top_run(mrb_state *mrb, struct RProc *proc, mrb_value self, unsigned int sta
     return mrb_vm_run(mrb, proc, self, stack_keep);
   }
   if (mrb->c->ci == mrb->c->cibase) {
-    mrb->c->ci->env = NULL;
     return mrb_vm_run(mrb, proc, self, stack_keep);
   }
   ci = cipush(mrb);