gh-134584: Optimize _BINARY_OP_SUBSCR_LIST_SLICE (GH-144659)

Author: Sacul0457

Include/internal/pycore_opcode_metadata.h

@@ -3660,6 +3660,23 @@ def testfunc(n):
         self.assertLessEqual(count_ops(ex, "_POP_TOP_INT"), 1)
         self.assertIn("_POP_TOP_NOP", uops)
 
+    def test_binary_subscr_list_slice(self):
+        def testfunc(n):
+            x = 0
+            for _ in range(n):
+                l = [1, 2, 3]
+                x += l[0:1][0]
+            return x
+
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
+        uops = get_opnames(ex)
+
+        self.assertIn("_BINARY_OP_SUBSCR_LIST_SLICE", uops)
+        self.assertNotIn("_GUARD_TOS_LIST", uops)
+        self.assertEqual(count_ops(ex, "_POP_TOP"), 3)
+        self.assertEqual(count_ops(ex, "_POP_TOP_NOP"), 4)
+
     def test_is_op(self):
         def test_is_false(n):
             a = object()

Include/internal/pycore_uop_ids.h

@@ -0,0 +1 @@
+Optimize and eliminate ref-counting in ``_BINARY_OP_SUBSCR_LIST_SLICE``

Include/internal/pycore_uop_metadata.h

@@ -938,9 +938,9 @@ dummy_func(
         }
 
         macro(BINARY_OP_SUBSCR_LIST_SLICE) =
-            _GUARD_TOS_SLICE + _GUARD_NOS_LIST + unused/5 + _BINARY_OP_SUBSCR_LIST_SLICE;
+            _GUARD_TOS_SLICE + _GUARD_NOS_LIST + unused/5 + _BINARY_OP_SUBSCR_LIST_SLICE + POP_TOP + POP_TOP;
 
-        op(_BINARY_OP_SUBSCR_LIST_SLICE, (list_st, sub_st -- res)) {
+        op(_BINARY_OP_SUBSCR_LIST_SLICE, (list_st, sub_st -- res, ls, ss)) {
             PyObject *sub = PyStackRef_AsPyObjectBorrow(sub_st);
             PyObject *list = PyStackRef_AsPyObjectBorrow(list_st);
 
@@ -949,9 +949,13 @@ dummy_func(
 
             PyObject *res_o = _PyList_SliceSubscript(list, sub);
             STAT_INC(BINARY_OP, hit);
-            DECREF_INPUTS();
-            ERROR_IF(res_o == NULL);
+            if (res_o == NULL) {
+                ERROR_NO_POP();
+            }
             res = PyStackRef_FromPyObjectSteal(res_o);
+            ls = list_st;
+            ss = sub_st;
+            INPUTS_DEAD();
         }
 
         macro(BINARY_OP_SUBSCR_STR_INT) =

Lib/test/test_capi/test_opt.py

@@ -422,6 +422,12 @@ dummy_func(void) {
         ss = sub_st;
     }
 
+    op(_BINARY_OP_SUBSCR_LIST_SLICE, (list_st, sub_st -- res, ls, ss)) {
+        res = sym_new_type(ctx, &PyList_Type);
+        ls = list_st;
+        ss = sub_st;
+    }
+
     op(_TO_BOOL, (value -- res)) {
         int already_bool = optimize_to_bool(this_instr, ctx, value, &res, false);
         if (!already_bool) {