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, 3 insertions, 3 deletions

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 */