fix scaling of enums

Author: kumaraditya303

Python/specialize.c

@@ -1201,15 +1201,23 @@ specialize_class_load_attr(PyObject *owner, _Py_CODEUNIT *instr,
         }
     }
     switch (kind) {
-        case METHOD:
-        case NON_DESCRIPTOR:
-            #ifdef Py_GIL_DISABLED
-            if (!_PyObject_HasDeferredRefcount(descr)) {
-                SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_ATTR_DESCR_NOT_DEFERRED);
+        case MUTABLE:
+            // special case for enums which has Py_TYPE(descr) == cls
+            // so guarding on type_version is sufficient
+            if (Py_TYPE(descr) != cls) {
+                SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_ATTR_MUTABLE_CLASS);
                 Py_XDECREF(descr);
                 return -1;
             }
-            #endif
+            if (Py_TYPE(descr)->tp_descr_get || Py_TYPE(descr)->tp_descr_set) {
+                SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_ATTR_MUTABLE_CLASS);
+                Py_XDECREF(descr);
+                return -1;
+            }
+            _Py_FALLTHROUGH;
+        case METHOD:
+        case NON_DESCRIPTOR:
+            PyUnstable_Object_EnableDeferredRefcount(descr);
             write_u32(cache->type_version, tp_version);
             write_ptr(cache->descr, descr);
             if (metaclass_check) {

Tools/ftscalingbench/ftscalingbench.py

@@ -295,6 +295,27 @@ def setattr_non_interned():
         setattr(obj, f"{prefix}_c", None)
 
 
+from enum import Enum
+class MyEnum(Enum):
+    X = 1
+    Y = 2
+    Z = 3
+
+@register_benchmark
+def enum_attr():
+    for _ in range(1000 * WORK_SCALE):
+        MyEnum.X
+        MyEnum.Y
+        MyEnum.Z
+
+@register_benchmark
+def enum_value():
+    for _ in range(1000 * WORK_SCALE):
+        MyEnum.X.value
+        MyEnum.Y.value
+        MyEnum.Z.value
+
+
 def bench_one_thread(func):
     t0 = time.perf_counter_ns()
     func()