gh-134584: Eliminate redundant refcounting from _STORE_ATTR_INSTANCE_VALUE

Lib/test/test_capi/test_opt.py

@@ -2511,6 +2511,23 @@ def testfunc(n):
         self.assertNotIn("_GUARD_TOS_INT", uops)
         self.assertNotIn("_GUARD_NOS_INT", uops)
 
+    def test_store_attr_instance_value(self):
+        def testfunc(n):
+            class C:
+                pass
+            c = C()
+            for i in range(n):
+                c.a = i
+            return c.a
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD - 1)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+
+        self.assertIn("_STORE_ATTR_INSTANCE_VALUE", uops)
+        self.assertNotIn("_POP_TOP", uops)
+        self.assertIn("_POP_TOP_NOP", uops)
+
     def test_store_subscr_int(self):
         def testfunc(n):
             l = [0, 0, 0, 0]

Misc/NEWS.d/next/Core_and_Builtins/2025-12-16-01-17-21.gh-issue-134584.tsxYYw.rst

@@ -0,0 +1 @@
+Eliminate redundant refcounting from ``_STORE_ATTR_INSTANCE_VALUE``.

Python/bytecodes.c

@@ -2609,7 +2609,7 @@ dummy_func(
             }
         }
 
-        op(_STORE_ATTR_INSTANCE_VALUE, (offset/1, value, owner --)) {
+        op(_STORE_ATTR_INSTANCE_VALUE, (offset/1, value, owner -- o)) {
             PyObject *owner_o = PyStackRef_AsPyObjectBorrow(owner);
 
             STAT_INC(STORE_ATTR, hit);
@@ -2623,15 +2623,17 @@ dummy_func(
                 _PyDictValues_AddToInsertionOrder(values, index);
             }
             UNLOCK_OBJECT(owner_o);
-            PyStackRef_CLOSE(owner);
+            o = owner;
+            DEAD(owner);
             Py_XDECREF(old_value);
         }
 
         macro(STORE_ATTR_INSTANCE_VALUE) =
             unused/1 +
             _GUARD_TYPE_VERSION_AND_LOCK +
             _GUARD_DORV_NO_DICT +
-            _STORE_ATTR_INSTANCE_VALUE;
+            _STORE_ATTR_INSTANCE_VALUE +
+            POP_TOP;
 
         op(_STORE_ATTR_WITH_HINT, (hint/1, value, owner --)) {
             PyObject *owner_o = PyStackRef_AsPyObjectBorrow(owner);

Python/optimizer_bytecodes.c

@@ -99,6 +99,11 @@ dummy_func(void) {
         GETLOCAL(oparg) = temp;
     }
 
+    op(_STORE_ATTR_INSTANCE_VALUE, (offset/1, value, owner -- o)) {
+        (void)value;
+        o = owner;
+    }
+
     op(_STORE_FAST, (value --)) {
         GETLOCAL(oparg) = value;
     }