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`.

1 files changed, 2 insertions, 2 deletions

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);