RTypedData: keep direct reference to IMEMO/fields

Similar to f3206cc79b but for TypedData.

It's quite common for TypedData objects to have a mix of reference in
their struct and some ivars.
Since we do happen to have 8B free in the RtypedData struct, we could
use it to keep a direct reference to the IMEMO/fields saving having
to synchronize the VM and lookup the `gen_fields_tbl` on every ivar
access.

For old school Data classes however, we don't have free space, but
this API is soft-deprecated and no longer very common.

gc.c

@@ -1047,7 +1047,7 @@ rb_data_object_wrap(VALUE klass, void *datap, RUBY_DATA_FUNC dmark, RUBY_DATA_FU
 {
     RUBY_ASSERT_ALWAYS(dfree != (RUBY_DATA_FUNC)1);
     if (klass) rb_data_object_check(klass);
-    return newobj_of(GET_RACTOR(), klass, T_DATA, (VALUE)dmark, (VALUE)datap, (VALUE)dfree, !dmark, sizeof(struct RTypedData));
+    return newobj_of(GET_RACTOR(), klass, T_DATA, (VALUE)dmark, (VALUE)dfree, (VALUE)datap, !dmark, sizeof(struct RTypedData));
 }
 
 VALUE
@@ -1064,7 +1064,7 @@ typed_data_alloc(VALUE klass, VALUE typed_flag, void *datap, const rb_data_type_
     RBIMPL_NONNULL_ARG(type);
     if (klass) rb_data_object_check(klass);
     bool wb_protected = (type->flags & RUBY_FL_WB_PROTECTED) || !type->function.dmark;
-    return newobj_of(GET_RACTOR(), klass, T_DATA, ((VALUE)type) | IS_TYPED_DATA | typed_flag, (VALUE)datap, 0, wb_protected, size);
+    return newobj_of(GET_RACTOR(), klass, T_DATA, 0, ((VALUE)type) | IS_TYPED_DATA | typed_flag, (VALUE)datap, wb_protected, size);
 }
 
 VALUE
@@ -3173,10 +3173,15 @@ rb_gc_mark_children(void *objspace, VALUE obj)
         break;
 
       case T_DATA: {
-        void *const ptr = RTYPEDDATA_P(obj) ? RTYPEDDATA_GET_DATA(obj) : DATA_PTR(obj);
+        bool typed_data = RTYPEDDATA_P(obj);
+        void *const ptr = typed_data ? RTYPEDDATA_GET_DATA(obj) : DATA_PTR(obj);
+
+        if (typed_data) {
+            gc_mark_internal(RTYPEDDATA(obj)->fields_obj);
+        }
 
         if (ptr) {
-            if (RTYPEDDATA_P(obj) && gc_declarative_marking_p(RTYPEDDATA_TYPE(obj))) {
+            if (typed_data && gc_declarative_marking_p(RTYPEDDATA_TYPE(obj))) {
                 size_t *offset_list = TYPED_DATA_REFS_OFFSET_LIST(obj);
 
                 for (size_t offset = *offset_list; offset != RUBY_REF_END; offset = *offset_list++) {
@@ -3184,7 +3189,7 @@ rb_gc_mark_children(void *objspace, VALUE obj)
                 }
             }
             else {
-                RUBY_DATA_FUNC mark_func = RTYPEDDATA_P(obj) ?
+                RUBY_DATA_FUNC mark_func = typed_data ?
                     RTYPEDDATA_TYPE(obj)->function.dmark :
                     RDATA(obj)->dmark;
                 if (mark_func) (*mark_func)(ptr);
@@ -4121,9 +4126,15 @@ rb_gc_update_object_references(void *objspace, VALUE obj)
       case T_DATA:
         /* Call the compaction callback, if it exists */
         {
-            void *const ptr = RTYPEDDATA_P(obj) ? RTYPEDDATA_GET_DATA(obj) : DATA_PTR(obj);
+            bool typed_data = RTYPEDDATA_P(obj);
+            void *const ptr = typed_data ? RTYPEDDATA_GET_DATA(obj) : DATA_PTR(obj);
+
+            if (typed_data) {
+                UPDATE_IF_MOVED(objspace, RTYPEDDATA(obj)->fields_obj);
+            }
+
             if (ptr) {
-                if (RTYPEDDATA_P(obj) && gc_declarative_marking_p(RTYPEDDATA_TYPE(obj))) {
+                if (typed_data && gc_declarative_marking_p(RTYPEDDATA_TYPE(obj))) {
                     size_t *offset_list = TYPED_DATA_REFS_OFFSET_LIST(obj);
 
                     for (size_t offset = *offset_list; offset != RUBY_REF_END; offset = *offset_list++) {
@@ -4131,7 +4142,7 @@ rb_gc_update_object_references(void *objspace, VALUE obj)
                         *ref = gc_location_internal(objspace, *ref);
                     }
                 }
-                else if (RTYPEDDATA_P(obj)) {
+                else if (typed_data) {
                     RUBY_DATA_FUNC compact_func = RTYPEDDATA_TYPE(obj)->function.dcompact;
                     if (compact_func) (*compact_func)(ptr);
                 }

include/ruby/internal/abi.h

@@ -24,7 +24,7 @@
  * In released versions of Ruby, this number is not defined since teeny
  * versions of Ruby should guarantee ABI compatibility.
  */
-#define RUBY_ABI_VERSION 2
+#define RUBY_ABI_VERSION 3
 
 /* Windows does not support weak symbols so ruby_abi_version will not exist
  * in the shared library. */

include/ruby/internal/core/rdata.h

@@ -133,12 +133,6 @@ struct RData {
      */
     RUBY_DATA_FUNC dmark;
 
-    /** Pointer to the actual C level struct that you want to wrap.
-      * This is in between dmark and dfree to allow DATA_PTR to continue
-      * to work for both RData and non-embedded RTypedData.
-      */
-    void *data;
-
     /**
      * This function is called when the object  is no longer used.  You need to
      * do whatever necessary to avoid memory leaks.
@@ -147,6 +141,12 @@ struct RData {
      *           impossible at that moment (that is why GC runs).
      */
     RUBY_DATA_FUNC dfree;
+
+    /** Pointer to the actual C level struct that you want to wrap.
+      * This is in between dmark and dfree to allow DATA_PTR to continue
+      * to work for both RData and non-embedded RTypedData.
+      */
+    void *data;
 };
 
 RBIMPL_SYMBOL_EXPORT_BEGIN()

include/ruby/internal/core/rtypeddata.h

@@ -355,6 +355,9 @@ struct RTypedData {
     /** The part that all ruby objects have in common. */
     struct RBasic basic;
 
+    /** Direct reference to the slots that holds instance variables, if any **/
+    VALUE fields_obj;
+
     /**
      * This is a `const rb_data_type_t *const` value, with the low bits set:
      *

variable.c

@@ -1231,13 +1231,20 @@ rb_obj_fields(VALUE obj, ID field_name)
     VALUE fields_obj = 0;
     if (rb_shape_obj_has_fields(obj)) {
         switch (BUILTIN_TYPE(obj)) {
+          case T_DATA:
+            if (LIKELY(RTYPEDDATA_P(obj))) {
+                fields_obj = RTYPEDDATA(obj)->fields_obj;
+                break;
+            }
+            goto generic_fields;
           case T_STRUCT:
             if (LIKELY(!FL_TEST_RAW(obj, RSTRUCT_GEN_FIELDS))) {
                 fields_obj = RSTRUCT_FIELDS_OBJ(obj);
                 break;
             }
-            // fall through
+            goto generic_fields;
           default:
+          generic_fields:
             RB_VM_LOCKING() {
                 if (!st_lookup(generic_fields_tbl_, (st_data_t)obj, (st_data_t *)&fields_obj)) {
                     rb_bug("Object is missing entry in generic_fields_tbl");
@@ -1254,13 +1261,20 @@ rb_free_generic_ivar(VALUE obj)
     if (rb_obj_exivar_p(obj)) {
         st_data_t key = (st_data_t)obj, value;
         switch (BUILTIN_TYPE(obj)) {
+          case T_DATA:
+            if (LIKELY(RTYPEDDATA_P(obj))) {
+                RB_OBJ_WRITE(obj, &RTYPEDDATA(obj)->fields_obj, 0);
+                break;
+            }
+            goto generic_fields;
           case T_STRUCT:
             if (LIKELY(!FL_TEST_RAW(obj, RSTRUCT_GEN_FIELDS))) {
                 RSTRUCT_SET_FIELDS_OBJ(obj, 0);
                 break;
             }
-            // fall through
+            goto generic_fields;
           default:
+          generic_fields:
             RB_VM_LOCKING() {
                 st_delete(generic_fields_tbl_no_ractor_check(), &key, &value);
             }
@@ -1279,13 +1293,20 @@ rb_obj_set_fields(VALUE obj, VALUE fields_obj, ID field_name, VALUE original_fie
 
     if (fields_obj != original_fields_obj) {
         switch (BUILTIN_TYPE(obj)) {
+          case T_DATA:
+            if (LIKELY(RTYPEDDATA_P(obj))) {
+                RB_OBJ_WRITE(obj, &RTYPEDDATA(obj)->fields_obj, fields_obj);
+                break;
+            }
+            goto generic_fields;
           case T_STRUCT:
             if (LIKELY(!FL_TEST_RAW(obj, RSTRUCT_GEN_FIELDS))) {
                 RSTRUCT_SET_FIELDS_OBJ(obj, fields_obj);
                 break;
             }
-            // fall through
+            goto generic_fields;
           default:
+          generic_fields:
             RB_VM_LOCKING() {
                 st_insert(generic_fields_tbl_, (st_data_t)obj, (st_data_t)fields_obj);
             }