Move `attached_object` into `rb_classext_struct`

Given that signleton classes don't have an allocator,
we can re-use these bytes to store the attached object
in `rb_classext_struct` without making it larger.

1 files changed, 27 insertions, 5 deletions

diff --git a/internal/class.h b/internal/class.h
index b777548174..9905e4e388 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -53,7 +53,14 @@ struct rb_classext_struct {
     struct rb_subclass_entry *module_subclass_entry;
     const VALUE origin_;
     const VALUE refined_class;
-    rb_alloc_func_t allocator;
+    union {
+        struct {
+            rb_alloc_func_t allocator;
+        } class;
+        struct {
+            VALUE attached_object;
+        } singleton_class;
+    } as;
     const VALUE includer;
 #if !SHAPE_IN_BASIC_FLAGS
     shape_id_t shape_id;
@@ -97,11 +104,10 @@ STATIC_ASSERT(sizeof_rb_classext_t, sizeof(struct RClass) + sizeof(rb_classext_t
 #define RCLASS_INCLUDER(c) (RCLASS_EXT(c)->includer)
 #define RCLASS_SUBCLASS_ENTRY(c) (RCLASS_EXT(c)->subclass_entry)
 #define RCLASS_MODULE_SUBCLASS_ENTRY(c) (RCLASS_EXT(c)->module_subclass_entry)
-#define RCLASS_ALLOCATOR(c) (RCLASS_EXT(c)->allocator)
 #define RCLASS_SUBCLASSES(c) (RCLASS_EXT(c)->subclasses)
 #define RCLASS_SUPERCLASS_DEPTH(c) (RCLASS_EXT(c)->superclass_depth)
 #define RCLASS_SUPERCLASSES(c) (RCLASS_EXT(c)->superclasses)
-#define RCLASS_ATTACHED_OBJECT(c) (rb_attr_get(c, id__attached__))
+#define RCLASS_ATTACHED_OBJECT(c) (RCLASS_EXT(c)->as.singleton_class.attached_object)
 
 #define RICLASS_IS_ORIGIN FL_USER0
 #define RCLASS_CLONED     FL_USER1
@@ -147,6 +153,22 @@ VALUE rb_class_inherited(VALUE, VALUE);
 VALUE rb_keyword_error_new(const char *, VALUE);
 MJIT_SYMBOL_EXPORT_END
 
+static inline rb_alloc_func_t
+RCLASS_ALLOCATOR(VALUE klass)
+{
+    if (FL_TEST_RAW(klass, FL_SINGLETON)) {
+        return NULL;
+    }
+    return RCLASS_EXT(klass)->as.class.allocator;
+}
+
+static inline void
+RCLASS_SET_ALLOCATOR(VALUE klass, rb_alloc_func_t allocator)
+{
+    assert(!FL_TEST(klass, FL_SINGLETON));
+    RCLASS_EXT(klass)->as.class.allocator = allocator;
+}
+
 static inline void
 RCLASS_SET_ORIGIN(VALUE klass, VALUE origin)
 {
@@ -204,9 +226,9 @@ static inline VALUE
 RCLASS_SET_ATTACHED_OBJECT(VALUE klass, VALUE attached_object)
 {
     assert(BUILTIN_TYPE(klass) == T_CLASS);
-    assert(FL_TEST(klass, FL_SINGLETON));
+    assert(FL_TEST_RAW(klass, FL_SINGLETON));
 
-    rb_class_ivar_set(klass, id__attached__, attached_object);
+    RB_OBJ_WRITE(klass, &RCLASS_EXT(klass)->as.singleton_class.attached_object, attached_object);
     return attached_object;
 }