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, 2 deletions

diff --git a/class.c b/class.c
index d181fb0b2e..85663ada50 100644
--- a/class.c
+++ b/class.c
@@ -197,7 +197,7 @@ class_alloc(VALUE flags, VALUE klass)
 {
     size_t alloc_size = sizeof(struct RClass);
 
-#if USE_RVARGC
+#if RCLASS_EXT_EMBEDDED
     alloc_size += sizeof(rb_classext_t);
 #endif
 
@@ -206,7 +206,7 @@ class_alloc(VALUE flags, VALUE klass)
     if (RGENGC_WB_PROTECTED_CLASS) flags |= FL_WB_PROTECTED;
     RVARGC_NEWOBJ_OF(obj, struct RClass, klass, flags, alloc_size);
 
-#if USE_RVARGC
+#if RCLASS_EXT_EMBEDDED
     memset(RCLASS_EXT(obj), 0, sizeof(rb_classext_t));
 #else
     obj->ptr = ZALLOC(rb_classext_t);