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`.

2 files changed, 4 insertions, 1 deletions

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;
   }