gh-134584: Eliminate redundant refcounting from _CALL_ISINSTANCE

Lib/test/test_capi/test_opt.py

@@ -2093,6 +2093,19 @@ def testfunc(n):
         self.assertNotIn("_POP_CALL_ONE_LOAD_CONST_INLINE_BORROW", uops)
         self.assertNotIn("_POP_CALL_TWO_LOAD_CONST_INLINE_BORROW", uops)
 
+    def test_call_isinstance_guards_pop_top(self):
+        def testfunc(n):
+            x = 0
+            for _ in range(n):
+                x += isinstance(42, int)
+            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("_POP_TOP_NOP", uops)
+
     def test_call_list_append(self):
         def testfunc(n):
             a = []

Misc/NEWS.d/next/Core_and_Builtins/2025-06-28-16-56-56.gh-issue-134584.Hnd1DZ.rst

@@ -0,0 +1,2 @@
+Eliminate redundant refcounting from ``_CALL_ISINSTANCE``. Patch by Noam
+Cohen

Python/bytecodes.c

@@ -4349,7 +4349,7 @@ dummy_func(
             DEOPT_IF(callable_o != interp->callable_cache.isinstance);
         }
 
-        op(_CALL_ISINSTANCE, (callable, null, instance, cls -- res)) {
+        op(_CALL_ISINSTANCE, (callable, null, instance, cls -- res, c1, i, c2)) {
             /* isinstance(o, o2) */
             STAT_INC(CALL, hit);
             PyObject *inst_o = PyStackRef_AsPyObjectBorrow(instance);
@@ -4358,11 +4358,10 @@ dummy_func(
             if (retval < 0) {
                 ERROR_NO_POP();
             }
-            (void)null; // Silence compiler warnings about unused variables
-            PyStackRef_CLOSE(cls);
-            PyStackRef_CLOSE(instance);
-            DEAD(null);
-            PyStackRef_CLOSE(callable);
+            INPUTS_DEAD();
+            c1 = callable;
+            i = instance;
+            c2 = cls;
             res = retval ? PyStackRef_True : PyStackRef_False;
             assert((!PyStackRef_IsNull(res)) ^ (_PyErr_Occurred(tstate) != NULL));
         }
@@ -4372,7 +4371,10 @@ dummy_func(
             unused/2 +
             _GUARD_THIRD_NULL +
             _GUARD_CALLABLE_ISINSTANCE +
-            _CALL_ISINSTANCE;
+            _CALL_ISINSTANCE +
+            POP_TOP +
+            POP_TOP +
+            POP_TOP;
 
         macro(CALL_LIST_APPEND) =
             unused/1 +
@@ -5360,6 +5362,19 @@ dummy_func(
             value = PyStackRef_FromPyObjectBorrow(ptr);
         }
 
+        tier2 op(_SWAP_CALL_TWO_LOAD_CONST_INLINE_BORROW, (ptr/4, callable, null, instance, cls -- value, c1, i, c2)) {
+            PyStackRef_CLOSE(cls);
+            PyStackRef_CLOSE(instance);
+            (void)null; // Silence compiler warnings about unused variables
+            DEAD(null);
+            PyStackRef_CLOSE(callable);
+            assert(_Py_IsImmortal(PyStackRef_AsPyObjectBorrow(callable)));
+            value = PyStackRef_FromPyObjectBorrow(ptr);
+            c1 = callable;
+            i = instance;
+            c2 = cls;
+        }
+
         tier2 op(_LOAD_CONST_UNDER_INLINE, (ptr/4, old -- value, new)) {
             new = old;
             DEAD(old);

Python/optimizer_analysis.c

@@ -567,6 +567,7 @@ const uint16_t op_without_push[MAX_UOP_ID + 1] = {
     [_POP_TOP_LOAD_CONST_INLINE_BORROW] = _POP_TOP,
     [_POP_TWO_LOAD_CONST_INLINE_BORROW] = _POP_TWO,
     [_POP_CALL_TWO_LOAD_CONST_INLINE_BORROW] = _POP_CALL_TWO,
+    [_SWAP_CALL_TWO_LOAD_CONST_INLINE_BORROW] = _POP_CALL_TWO_LOAD_CONST_INLINE_BORROW,
 };
 
 const bool op_skip[MAX_UOP_ID + 1] = {

Python/optimizer_bytecodes.c

@@ -567,6 +567,13 @@ dummy_func(void) {
         value = PyJitRef_Borrow(sym_new_const(ctx, ptr));
     }
 
+    op(_SWAP_CALL_TWO_LOAD_CONST_INLINE_BORROW, (ptr/4, callable, null, instance, cls -- value, c1, i, c2)) {
+        value = PyJitRef_Borrow(sym_new_const(ctx, ptr));
+        c1 = callable;
+        i = instance;
+        c2 = cls;
+    }
+
     op(_POP_TOP, (value -- )) {
         PyTypeObject *typ = sym_get_type(value);
         if (PyJitRef_IsBorrowed(value) ||
@@ -997,7 +1004,7 @@ dummy_func(void) {
         }
     }
 
-    op(_CALL_ISINSTANCE, (unused, unused, instance, cls -- res)) {
+    op(_CALL_ISINSTANCE, (unused, unused, instance, cls -- res, unused, unused, unused)) {
         // the result is always a bool, but sometimes we can
         // narrow it down to True or False
         res = sym_new_type(ctx, &PyBool_Type);
@@ -1013,7 +1020,7 @@ dummy_func(void) {
                 out = Py_True;
             }
             sym_set_const(res, out);
-            REPLACE_OP(this_instr, _POP_CALL_TWO_LOAD_CONST_INLINE_BORROW, 0, (uintptr_t)out);
+            REPLACE_OP(this_instr, _SWAP_CALL_TWO_LOAD_CONST_INLINE_BORROW, 0, (uintptr_t)out);
         }
     }