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 <tenderlove@ruby-lang.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/internal/variable.h b/internal/variable.h
index 734884a5f6..553e87c4a8 100644
--- a/internal/variable.h
+++ b/internal/variable.h
@@ -13,6 +13,7 @@
 #include "constant.h"           /* for rb_const_entry_t */
 #include "ruby/internal/stdbool.h"     /* for bool */
 #include "ruby/ruby.h"          /* for VALUE */
+#include "shape.h"              /* for rb_shape_t */
 
 /* global variable */
 
@@ -53,7 +54,7 @@ VALUE rb_gvar_get(ID);
 VALUE rb_gvar_set(ID, VALUE);
 VALUE rb_gvar_defined(ID);
 void rb_const_warn_if_deprecated(const rb_const_entry_t *, VALUE, ID);
-void rb_init_iv_list(VALUE obj);
+rb_shape_t * rb_grow_iv_list(VALUE obj);
 void rb_ensure_iv_list_size(VALUE obj, uint32_t len, uint32_t newsize);
 struct gen_ivtbl * rb_ensure_generic_iv_list_size(VALUE obj, uint32_t newsize);
 MJIT_SYMBOL_EXPORT_END