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, 5 insertions, 2 deletions

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);
 }