This commit implements the Object Shapes technique in CRuby.

Object Shapes is used for accessing instance variables and representing the
"frozenness" of objects.  Object instances have a "shape" and the shape
represents some attributes of the object (currently which instance variables are
set and the "frozenness").  Shapes form a tree data structure, and when a new
instance variable is set on an object, that object "transitions" to a new shape
in the shape tree.  Each shape has an ID that is used for caching. The shape
structure is independent of class, so objects of different types can have the
same shape.

For example:

```ruby
class Foo
  def initialize
    # Starts with shape id 0
    @a = 1 # transitions to shape id 1
    @b = 1 # transitions to shape id 2
  end
end

class Bar
  def initialize
    # Starts with shape id 0
    @a = 1 # transitions to shape id 1
    @b = 1 # transitions to shape id 2
  end
end

foo = Foo.new # `foo` has shape id 2
bar = Bar.new # `bar` has shape id 2
```

Both `foo` and `bar` instances have the same shape because they both set
instance variables of the same name in the same order.

This technique can help to improve inline cache hits as well as generate more
efficient machine code in JIT compilers.

This commit also adds some methods for debugging shapes on objects.  See
`RubyVM::Shape` for more details.

For more context on Object Shapes, see [Feature: #18776]

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Co-Authored-By: Eileen M. Uchitelle <eileencodes@gmail.com>
Co-Authored-By: John Hawthorn <john@hawthorn.email>

1 files changed, 0 insertions, 22 deletions

diff --git a/internal/object.h b/internal/object.h
index 88f3a44bc6..7b54e13dd2 100644
--- a/internal/object.h
+++ b/internal/object.h
@@ -9,11 +9,6 @@
  * @brief      Internal header for Object.
  */
 #include "ruby/ruby.h"          /* for VALUE */
-#include "internal/class.h"     /* for RCLASS_IV_INDEX_TBL */
-
-#ifdef ROBJECT_IV_INDEX_TBL
-# undef ROBJECT_IV_INDEX_TBL
-#endif
 
 /* object.c */
 VALUE rb_class_search_ancestor(VALUE klass, VALUE super);
@@ -26,7 +21,6 @@ int rb_bool_expected(VALUE, const char *, int raise);
 static inline void RBASIC_CLEAR_CLASS(VALUE obj);
 static inline void RBASIC_SET_CLASS_RAW(VALUE obj, VALUE klass);
 static inline void RBASIC_SET_CLASS(VALUE obj, VALUE klass);
-static inline struct st_table *ROBJECT_IV_INDEX_TBL_inline(VALUE obj);
 
 RUBY_SYMBOL_EXPORT_BEGIN
 /* object.c (export) */
@@ -64,20 +58,4 @@ RBASIC_SET_CLASS(VALUE obj, VALUE klass)
     RBASIC_SET_CLASS_RAW(obj, klass);
     RB_OBJ_WRITTEN(obj, oldv, klass);
 }
-
-RBIMPL_ATTR_PURE()
-static inline struct st_table *
-ROBJECT_IV_INDEX_TBL_inline(VALUE obj)
-{
-    if (RB_FL_ANY_RAW(obj, ROBJECT_EMBED)) {
-        VALUE klass = rb_obj_class(obj);
-        return RCLASS_IV_INDEX_TBL(klass);
-    }
-    else {
-        const struct RObject *const ptr = ROBJECT(obj);
-        return ptr->as.heap.iv_index_tbl;
-    }
-}
-#define ROBJECT_IV_INDEX_TBL ROBJECT_IV_INDEX_TBL_inline
-
 #endif /* INTERNAL_OBJECT_H */