Fix refcount accounting

Author: markshannon

Include/internal/pycore_stackref.h

@@ -402,7 +402,7 @@ static inline void PyStackRef_CheckValid(_PyStackRef ref) {
         case 0:
         case Py_TAG_REFCNT:
             /* Can be immortal if object was made immortal after reference came into existence */
-            assert(obj != NULL && obj != Py_True && obj != Py_False && obj != Py_None);
+            assert(!_Py_IsStaticImmortal(obj));
             break;
         case Py_TAG_IMMORTAL:
             assert(obj == NULL || _Py_IsImmortal(obj));

Include/refcount.h

@@ -391,9 +391,7 @@ static inline void Py_DECREF_MORTAL(const char *filename, int lineno, PyObject *
     }
     _Py_DECREF_STAT_INC();
     assert(!_Py_IsStaticImmortal(op));
-    if (!_Py_IsImmortal(op)) {
-        _Py_DECREF_DecRefTotal();
-    }
+    _Py_DECREF_DecRefTotal();
     if (--op->ob_refcnt == 0) {
         _Py_Dealloc(op);
     }
@@ -409,9 +407,7 @@ static inline void _Py_DECREF_MORTAL_SPECIALIZED(const char *filename, int linen
     }
     _Py_DECREF_STAT_INC();
     assert(!_Py_IsStaticImmortal(op));
-    if (!_Py_IsImmortal(op)) {
-        _Py_DECREF_DecRefTotal();
-    }
+    _Py_DECREF_DecRefTotal();
     if (--op->ob_refcnt == 0) {
         destruct(op);
     }