gh-134584: Eliminate redundant refcounting from _CALL_STR_1

Signed-off-by: Manjusaka <me@manjusaka.me>

Author: Zheaoli

Include/internal/pycore_opcode_metadata.h

@@ -1858,6 +1858,20 @@ def testfunc(n):
         self.assertNotIn("_GUARD_NOS_NULL", uops)
         self.assertNotIn("_GUARD_CALLABLE_STR_1", uops)
 
+    def test_call_str_1_pop_top(self):
+        def testfunc(n):
+            x = 0
+            for _ in range(n):
+                t = str("")
+                x += 1 if len(t) == 0 else 0
+            return x
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+        self.assertIn("_CALL_STR_1", uops)
+        self.assertIn("_POP_TOP_NOP", uops)
+
     def test_call_str_1_result_is_str(self):
         def testfunc(n):
             x = 0

Lib/test/test_capi/test_opt.py

@@ -0,0 +1 @@
+Eliminate redundant refcounting from ``_CALL_STR_1``.

Misc/NEWS.d/next/Core_and_Builtins/2025-06-28-17-54-27.gh-issue-134584.EXgPub.rst

@@ -4055,17 +4055,14 @@ dummy_func(
             DEOPT_IF(callable_o != (PyObject *)&PyUnicode_Type);
         }
 
-        op(_CALL_STR_1, (callable, null, arg -- res)) {
+        op(_CALL_STR_1, (callable, null, arg -- res, a)) {
             PyObject *arg_o = PyStackRef_AsPyObjectBorrow(arg);
 
             assert(oparg == 1);
             STAT_INC(CALL, hit);
+            INPUTS_DEAD();
             PyObject *res_o = PyObject_Str(arg_o);
-            DEAD(null);
-            DEAD(callable);
-            (void)callable; // Silence compiler warnings about unused variables
-            (void)null;
-            PyStackRef_CLOSE(arg);
+            a = arg;
             ERROR_IF(res_o == NULL);
             res = PyStackRef_FromPyObjectSteal(res_o);
         }
@@ -4076,6 +4073,7 @@ dummy_func(
             _GUARD_NOS_NULL +
             _GUARD_CALLABLE_STR_1 +
             _CALL_STR_1 +
+            POP_TOP +
             _CHECK_PERIODIC;
 
         op(_GUARD_CALLABLE_TUPLE_1, (callable, unused, unused -- callable, unused, unused)) {

Python/bytecodes.c

@@ -936,14 +936,15 @@ dummy_func(void) {
         }
     }
 
-    op(_CALL_STR_1, (unused, unused, arg -- res)) {
+    op(_CALL_STR_1, (unused, unused, arg -- res, a)) {
         if (sym_matches_type(arg, &PyUnicode_Type)) {
             // e.g. str('foo') or str(foo) where foo is known to be a string
             res = arg;
         }
         else {
             res = sym_new_type(ctx, &PyUnicode_Type);
         }
+        a = arg;
     }
 
     op(_CALL_ISINSTANCE, (unused, unused, instance, cls -- res)) {