Refactor VM root modules

This `st_table` is used to both mark and pin classes
defined from the C API. But `vm->mark_object_ary` already
does both much more efficiently.

Currently a Ruby process starts with 252 rooted classes,
which uses `7224B` in an `st_table` or `2016B` in an `RArray`.

So a baseline of 5kB saved, but since `mark_object_ary` is
preallocated with `1024` slots but only use `405` of them,
it's a net `7kB` save.

`vm->mark_object_ary` is also being refactored.

Prior to this changes, `mark_object_ary` was a regular `RArray`, but
since this allows for references to be moved, it was marked a second
time from `rb_vm_mark()` to pin these objects.

This has the detrimental effect of marking these references on every
minors even though it's a mostly append only list.

But using a custom TypedData we can save from having to mark
all the references on minor GC runs.

Addtionally, immediate values are now ignored and not appended
to `vm->mark_object_ary` as it's just wasted space.

1 files changed, 5 insertions, 3 deletions

diff --git a/variable.c b/variable.c
index eaedbc2d48..b484d65d19 100644
--- a/variable.c
+++ b/variable.c
@@ -72,11 +72,11 @@ Init_var_tables(void)
 
     autoload_mutex = rb_mutex_new();
     rb_obj_hide(autoload_mutex);
-    rb_gc_register_mark_object(autoload_mutex);
+    rb_vm_register_global_object(autoload_mutex);
 
     autoload_features = rb_ident_hash_new();
     rb_obj_hide(autoload_features);
-    rb_gc_register_mark_object(autoload_features);
+    rb_vm_register_global_object(autoload_features);
 }
 
 static inline bool
@@ -3701,7 +3701,9 @@ rb_define_const(VALUE klass, const char *name, VALUE val)
     if (!rb_is_const_id(id)) {
         rb_warn("rb_define_const: invalid name '%s' for constant", name);
     }
-    rb_gc_register_mark_object(val);
+    if (!RB_SPECIAL_CONST_P(val)) {
+        rb_vm_register_global_object(val);
+    }
     rb_const_set(klass, id, val);
 }