Implement embedded TypedData objects

This commit adds a new flag RUBY_TYPED_EMBEDDABLE that allows the data
of a TypedData object to be embedded after the object itself. This will
improve cache locality and allow us to save the 8 byte data pointer.

Co-Authored-By: Jean Boussier <byroot@ruby-lang.org>

error.c

@@ -1322,7 +1322,7 @@ rb_check_typeddata(VALUE obj, const rb_data_type_t *data_type)
         actual = rb_str_new_cstr(name); /* or rb_fstring_cstr? not sure... */
     }
     else {
-        return DATA_PTR(obj);
+        return RTYPEDDATA_GET_DATA(obj);
     }
 
     const char *expected = data_type->wrap_struct_name;

gc.c

@@ -3142,34 +3142,66 @@ rb_data_object_zalloc(VALUE klass, size_t size, RUBY_DATA_FUNC dmark, RUBY_DATA_
     return obj;
 }
 
-VALUE
-rb_data_typed_object_wrap(VALUE klass, void *datap, const rb_data_type_t *type)
+static VALUE
+typed_data_alloc(VALUE klass, VALUE typed_flag, void *datap, const rb_data_type_t *type, size_t size)
 {
     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, (VALUE)1, (VALUE)datap, wb_protected, sizeof(struct RTypedData));
+    return newobj_of(GET_RACTOR(), klass, T_DATA, (VALUE)type, 1 | typed_flag, (VALUE)datap, wb_protected, size);
+}
+
+VALUE
+rb_data_typed_object_wrap(VALUE klass, void *datap, const rb_data_type_t *type)
+{
+    if (UNLIKELY(type->flags & RUBY_TYPED_EMBEDDABLE)) {
+        rb_raise(rb_eTypeError, "Cannot wrap an embeddable TypedData");
+    }
+
+    return typed_data_alloc(klass, 0, datap, type, sizeof(struct RTypedData));
 }
 
 VALUE
 rb_data_typed_object_zalloc(VALUE klass, size_t size, const rb_data_type_t *type)
 {
-    VALUE obj = rb_data_typed_object_wrap(klass, 0, type);
+    if (type->flags & RUBY_TYPED_EMBEDDABLE) {
+        if (!(type->flags & RUBY_TYPED_FREE_IMMEDIATELY)) {
+            rb_raise(rb_eTypeError, "Embeddable TypedData must be freed immediately");
+        }
+
+        size_t embed_size = offsetof(struct RTypedData, data) + size;
+        if (rb_gc_size_allocatable_p(embed_size)) {
+            VALUE obj = typed_data_alloc(klass, TYPED_DATA_EMBEDDED, 0, type, embed_size);
+            memset((char *)obj + offsetof(struct RTypedData, data), 0, size);
+            return obj;
+        }
+    }
+
+    VALUE obj = typed_data_alloc(klass, 0, NULL, type, sizeof(struct RTypedData));
     DATA_PTR(obj) = xcalloc(1, size);
     return obj;
 }
 
 size_t
 rb_objspace_data_type_memsize(VALUE obj)
 {
+    size_t size = 0;
     if (RTYPEDDATA_P(obj)) {
         const rb_data_type_t *type = RTYPEDDATA_TYPE(obj);
         const void *ptr = RTYPEDDATA_DATA(obj);
+
+        if (RTYPEDDATA_TYPE(obj)->flags & RUBY_TYPED_EMBEDDABLE && !RTYPEDDATA_EMBEDDED_P(obj)) {
+#ifdef HAVE_MALLOC_USABLE_SIZE
+            size += malloc_usable_size((void *)ptr);
+#endif
+        }
+
         if (ptr && type->function.dsize) {
-            return type->function.dsize(ptr);
+            size += type->function.dsize(ptr);
         }
     }
-    return 0;
+
+    return size;
 }
 
 const char *
@@ -3454,17 +3486,23 @@ rb_data_free(rb_objspace_t *objspace, VALUE obj)
 
         if (dfree) {
             if (dfree == RUBY_DEFAULT_FREE) {
-                xfree(data);
-                RB_DEBUG_COUNTER_INC(obj_data_xfree);
+                if (!RTYPEDDATA_EMBEDDED_P(obj)) {
+                    xfree(data);
+                    RB_DEBUG_COUNTER_INC(obj_data_xfree);
+                }
             }
             else if (free_immediately) {
                 (*dfree)(data);
+                if (RTYPEDDATA_TYPE(obj)->flags & RUBY_TYPED_EMBEDDABLE && !RTYPEDDATA_EMBEDDED_P(obj)) {
+                    xfree(data);
+                }
+
                 RB_DEBUG_COUNTER_INC(obj_data_imm_free);
             }
             else {
-                RB_DEBUG_COUNTER_INC(obj_data_zombie);
                 make_zombie(objspace, obj, dfree, data);
-                return false;
+                RB_DEBUG_COUNTER_INC(obj_data_zombie);
+                return FALSE;
             }
         }
         else {
@@ -7313,7 +7351,8 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
 
       case T_DATA:
         {
-            void *const ptr = DATA_PTR(obj);
+            void *const ptr = RTYPEDDATA_P(obj) ? RTYPEDDATA_GET_DATA(obj) : DATA_PTR(obj);
+
             if (ptr) {
                 if (RTYPEDDATA_P(obj) && gc_declarative_marking_p(any->as.typeddata.type)) {
                     gc_mark_from_offset(objspace, obj);

include/ruby/internal/core/rtypeddata.h

@@ -114,6 +114,8 @@
 #define RUBY_TYPED_PROMOTED1         RUBY_TYPED_PROMOTED1
 /** @endcond */
 
+#define TYPED_DATA_EMBEDDED 2
+
 /**
  * @private
  *
@@ -137,6 +139,8 @@ rbimpl_typeddata_flags {
      */
     RUBY_TYPED_FREE_IMMEDIATELY = 1,
 
+    RUBY_TYPED_EMBEDDABLE = 2,
+
     /**
      * This flag has something to do with Ractor.  Multiple Ractors run without
      * protecting each  other.  Sharing  an object  among Ractors  is basically
@@ -460,7 +464,7 @@ RBIMPL_SYMBOL_EXPORT_END()
  */
 #define TypedData_Make_Struct0(result, klass, type, size, data_type, sval) \
     VALUE result = rb_data_typed_object_zalloc(klass, size, data_type);    \
-    (sval) = RBIMPL_CAST((type *)RTYPEDDATA_DATA(result));                  \
+    (sval) = RTYPEDDATA_GET_DATA(result); \
     RBIMPL_CAST(/*suppress unused variable warnings*/(void)(sval))
 
 /**
@@ -511,6 +515,36 @@ RBIMPL_SYMBOL_EXPORT_END()
 #define TypedData_Get_Struct(obj,type,data_type,sval) \
     ((sval) = RBIMPL_CAST((type *)rb_check_typeddata((obj), (data_type))))
 
+static inline bool
+RTYPEDDATA_EMBEDDED_P(VALUE obj)
+{
+#if RUBY_DEBUG
+    if (RB_UNLIKELY(!RB_TYPE_P(obj, RUBY_T_DATA))) {
+        Check_Type(obj, RUBY_T_DATA);
+        RBIMPL_UNREACHABLE_RETURN(false);
+    }
+#endif
+
+    return RTYPEDDATA(obj)->typed_flag & TYPED_DATA_EMBEDDED;
+}
+
+static inline void *
+RTYPEDDATA_GET_DATA(VALUE obj)
+{
+#if RUBY_DEBUG
+    if (RB_UNLIKELY(!RB_TYPE_P(obj, RUBY_T_DATA))) {
+        Check_Type(obj, RUBY_T_DATA);
+        RBIMPL_UNREACHABLE_RETURN(false);
+    }
+#endif
+
+    /* We reuse the data pointer in embedded TypedData. We can't use offsetof
+     * since RTypedData a non-POD type in C++. */
+    const size_t embedded_typed_data_size = sizeof(struct RTypedData) - sizeof(void *);
+
+    return RTYPEDDATA_EMBEDDED_P(obj) ? (char *)obj + embedded_typed_data_size : RTYPEDDATA(obj)->data;
+}
+
 RBIMPL_ATTR_PURE()
 RBIMPL_ATTR_ARTIFICIAL()
 /**
@@ -527,7 +561,8 @@ RBIMPL_ATTR_ARTIFICIAL()
 static inline bool
 rbimpl_rtypeddata_p(VALUE obj)
 {
-    return RTYPEDDATA(obj)->typed_flag == 1;
+    VALUE typed_flag = RTYPEDDATA(obj)->typed_flag;
+    return typed_flag != 0 && typed_flag <= 3;
 }
 
 RBIMPL_ATTR_PURE_UNLESS_DEBUG()