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, 11 deletions

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]);