Move IS_TYPED_DATA in RBasic.flags

Ref: ruby#14134 (comment)

We can't safely use low-bit pointer tagging anymore because `RTypedData.type`
lines up with `RData.dfree` and there is no aligment guarantee on function
pointers, as evidenced by `memcached` and `gpgme` gems.

We also can't use FL_USER* for this, because extensions may use these
for other purposes.

Using a general flag for this is a bit unfortunate, as general flags
are hard to come by, however I recently freed several of them, and
we still have two or three free ones left.

Author: byroot

gc.c

@@ -1062,7 +1062,7 @@ 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, 0, ((VALUE)type) | IS_TYPED_DATA | typed_flag, (VALUE)datap, wb_protected, size);
+    return newobj_of(GET_RACTOR(), klass, T_DATA | RUBY_TYPED_FL_IS_TYPED_DATA, 0, ((VALUE)type) | typed_flag, (VALUE)datap, wb_protected, size);
 }
 
 VALUE

include/ruby/internal/core/rtypeddata.h

@@ -115,10 +115,8 @@
 #define RUBY_TYPED_PROMOTED1         RUBY_TYPED_PROMOTED1
 /** @endcond */
 
-#define IS_TYPED_DATA ((VALUE)1)
-#define TYPED_DATA_EMBEDDED ((VALUE)2)
-#define TYPED_DATA_PTR_FLAGS ((VALUE)3)
-#define TYPED_DATA_PTR_MASK (~TYPED_DATA_PTR_FLAGS)
+#define TYPED_DATA_EMBEDDED ((VALUE)1)
+#define TYPED_DATA_PTR_MASK (~(TYPED_DATA_EMBEDDED))
 
 /**
  * @private
@@ -181,9 +179,9 @@ rbimpl_typeddata_flags {
     RUBY_TYPED_WB_PROTECTED     = RUBY_FL_WB_PROTECTED, /* THIS FLAG DEPENDS ON Ruby version */
 
     /**
-     * This flag no longer in use
+     * This flag is used to distinguish RTypedData from deprecated RData objects.
      */
-    RUBY_TYPED_UNUSED           = RUBY_FL_UNUSED6,
+    RUBY_TYPED_FL_IS_TYPED_DATA = RUBY_FL_USERPRIV0,
 
     /**
      * This flag determines whether marking and compaction should be carried out
@@ -569,7 +567,7 @@ RBIMPL_ATTR_ARTIFICIAL()
 static inline bool
 rbimpl_rtypeddata_p(VALUE obj)
 {
-    return RTYPEDDATA(obj)->type & IS_TYPED_DATA;
+    return FL_TEST_RAW(obj, RUBY_TYPED_FL_IS_TYPED_DATA);
 }
 
 RBIMPL_ATTR_PURE_UNLESS_DEBUG()

include/ruby/internal/fl_type.h

@@ -217,11 +217,11 @@ ruby_fl_type {
     RUBY_FL_PROMOTED    = (1<<5),
 
     /**
-     * This flag is no longer in use
+     * This flag meaning is type dependent, currently only used by T_DATA.
      *
      * @internal
      */
-    RUBY_FL_UNUSED6    = (1<<6),
+    RUBY_FL_USERPRIV0    = (1<<6),
 
     /**
      * This flag has  something to do with finalisers.  A  ruby object can have