gh-134584: Eliminate redundant refcounting from STORE_SUBSCR_LIST_INT

Author: corona10

Include/internal/pycore_opcode_metadata.h

@@ -2362,6 +2362,21 @@ def testfunc(n):
         self.assertNotIn("_GUARD_TOS_INT", uops)
         self.assertNotIn("_GUARD_NOS_INT", uops)
 
+    def test_store_subscr_int(self):
+        def testfunc(args):
+            n = args[0]
+            l = [0] * n
+            ret = 0
+            for idx in range(n):
+                l[idx] = idx
+            return sum(l)
+
+        res, ex = self._run_with_optimizer(testfunc, (TIER2_THRESHOLD,))
+        self.assertEqual(res, sum(range(TIER2_THRESHOLD)))
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+        self.assertIn("_POP_TOP_INT", uops)
+
     def test_attr_promotion_failure(self):
         # We're not testing for any specific uops here, just
         # testing it doesn't crash.

Lib/test/test_capi/test_opt.py

@@ -1121,9 +1121,9 @@ dummy_func(
         macro(STORE_SUBSCR) = _SPECIALIZE_STORE_SUBSCR + _STORE_SUBSCR;
 
         macro(STORE_SUBSCR_LIST_INT) =
-            _GUARD_TOS_INT + _GUARD_NOS_LIST + unused/1 + _STORE_SUBSCR_LIST_INT;
+            _GUARD_TOS_INT + _GUARD_NOS_LIST + unused/1 + _STORE_SUBSCR_LIST_INT + _POP_TOP_INT;
 
-        op(_STORE_SUBSCR_LIST_INT, (value, list_st, sub_st -- )) {
+        op(_STORE_SUBSCR_LIST_INT, (value, list_st, sub_st -- ss)) {
             PyObject *sub = PyStackRef_AsPyObjectBorrow(sub_st);
             PyObject *list = PyStackRef_AsPyObjectBorrow(list_st);
 
@@ -1146,8 +1146,8 @@ dummy_func(
                                         PyStackRef_AsPyObjectSteal(value));
             assert(old_value != NULL);
             UNLOCK_OBJECT(list);  // unlock before decrefs!
-            PyStackRef_CLOSE_SPECIALIZED(sub_st, _PyLong_ExactDealloc);
             DEAD(sub_st);
+            ss = sub_st;
             PyStackRef_CLOSE(list_st);
             Py_DECREF(old_value);
         }

Python/bytecodes.c

@@ -567,6 +567,13 @@ dummy_func(void) {
         value = PyJitRef_Borrow(sym_new_const(ctx, ptr));
     }
 
+    op(_POP_TOP_INT, (value -- )) {
+        if (PyJitRef_IsBorrowed(value) ||
+            sym_is_immortal(PyJitRef_Unwrap(value))) {
+            REPLACE_OP(this_instr, _POP_TOP_NOP, 0, 0);
+        }
+    }
+
     op(_POP_TOP, (value -- )) {
         PyTypeObject *typ = sym_get_type(value);
         if (PyJitRef_IsBorrowed(value) ||