Transition shape when object's capacity changes

This commit adds a `capacity` field to shapes, and adds shape
transitions whenever an object's capacity changes. Objects which are
allocated out of a bigger size pool will also make a transition from the
root shape to the shape with the correct capacity for their size pool
when they are allocated.

This commit will allow us to remove numiv from objects completely, and
will also mean we can guarantee that if two objects share shapes, their
IVs are in the same positions (an embedded and extended object cannot
share shapes). This will enable us to implement ivar sets in YJIT using
object shapes.

Co-Authored-By: Aaron Patterson <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/gc.h b/gc.h
index e1ce802095..b2356444c6 100644
--- a/gc.h
+++ b/gc.h
@@ -120,6 +120,8 @@ VALUE rb_gc_disable_no_rest(void);
 
 struct rb_thread_struct;
 
+size_t rb_size_pool_slot_size(unsigned char pool_id);
+
 RUBY_SYMBOL_EXPORT_BEGIN
 
 /* exports for objspace module */