Remove RGENGC_OLD_NEWOBJ_CHECK

The code doesn't compile, so probably nobody is using this.

Author: peterzhu2118

.github/workflows/compilers.yml

@@ -197,7 +197,6 @@ jobs:
 #         - { name: RGENGC_ESTIMATE_OLDMALLOC,      env: { cppflags: '-DRGENGC_ESTIMATE_OLDMALLOC' } }
 #         - { name: RGENGC_FORCE_MAJOR_GC,          env: { cppflags: '-DRGENGC_FORCE_MAJOR_GC' } }
 #         - { name: RGENGC_OBJ_INFO,                env: { cppflags: '-DRGENGC_OBJ_INFO' } }
-#         - { name: RGENGC_OLD_NEWOBJ_CHECK,        env: { cppflags: '-DRGENGC_OLD_NEWOBJ_CHECK' } }
 #         - { name: RGENGC_PROFILE,                 env: { cppflags: '-DRGENGC_PROFILE' } }
 
 #         - { name: VM_DEBUG_BP_CHECK,              env: { cppflags: '-DVM_DEBUG_BP_CHECK' } }

gc.c

@@ -431,16 +431,6 @@ int ruby_rgengc_debug;
 // Note: using RUBY_ASSERT_WHEN() extend a macro in expr (info by nobu).
 #define GC_ASSERT(expr) RUBY_ASSERT_MESG_WHEN(RGENGC_CHECK_MODE > 0, expr, #expr)
 
-/* RGENGC_OLD_NEWOBJ_CHECK
- * 0:  disable all assertions
- * >0: make a OLD object when new object creation.
- *
- * Make one OLD object per RGENGC_OLD_NEWOBJ_CHECK WB protected objects creation.
- */
-#ifndef RGENGC_OLD_NEWOBJ_CHECK
-#define RGENGC_OLD_NEWOBJ_CHECK 0
-#endif
-
 /* RGENGC_PROFILE
  * 0: disable RGenGC profiling
  * 1: enable profiling for basic information
@@ -2535,24 +2525,6 @@ newobj_init(VALUE klass, VALUE flags, int wb_protected, rb_objspace_t *objspace,
 
     gc_report(5, objspace, "newobj: %s\n", obj_info(obj));
 
-#if RGENGC_OLD_NEWOBJ_CHECK > 0
-    {
-        static int newobj_cnt = RGENGC_OLD_NEWOBJ_CHECK;
-
-        if (!is_incremental_marking(objspace) &&
-            flags & FL_WB_PROTECTED &&   /* do not promote WB unprotected objects */
-            ! RB_TYPE_P(obj, T_ARRAY)) { /* array.c assumes that allocated objects are new */
-            if (--newobj_cnt == 0) {
-                newobj_cnt = RGENGC_OLD_NEWOBJ_CHECK;
-
-                gc_mark_set(objspace, obj);
-                RVALUE_AGE_SET_OLD(objspace, obj);
-
-                rb_gc_writebarrier_remember(obj);
-            }
-        }
-    }
-#endif
     // RUBY_DEBUG_LOG("obj:%p (%s)", (void *)obj, obj_type_name(obj));
     return obj;
 }