gh-139757: Fix unintended bytecode specialization for non-ascii string

Lib/test/test_opcache.py

@@ -1785,6 +1785,15 @@ def binary_subscr_str_int():
         self.assert_specialized(binary_subscr_str_int, "BINARY_OP_SUBSCR_STR_INT")
         self.assert_no_opcode(binary_subscr_str_int, "BINARY_OP")
 
+        def binary_subscr_str_int_non_compact():
+            for _ in range(_testinternalcapi.SPECIALIZATION_THRESHOLD):
+                a = "바이트코드_특수화"
+                for idx, expected in enumerate(a):
+                    self.assertEqual(a[idx], expected)
+
+        binary_subscr_str_int_non_compact()
+        self.assert_no_opcode(binary_subscr_str_int_non_compact, "BINARY_OP_SUBSCR_STR_INT")
+
         def binary_subscr_getitems():
             class C:
                 def __init__(self, val):

Misc/NEWS.d/next/Core_and_Builtins/2026-01-02-22-35-12.gh-issue-139757.v5LRew.rst

@@ -0,0 +1,2 @@
+Fix unintended bytecode specialization for non-ascii string.
+Patch by Donghee Na, Ken Jin and Chris Eibl.

Python/specialize.c

@@ -2240,7 +2240,7 @@ _Py_Specialize_BinaryOp(_PyStackRef lhs_st, _PyStackRef rhs_st, _Py_CODEUNIT *in
                     specialize(instr, BINARY_OP_SUBSCR_TUPLE_INT);
                     return;
                 }
-                if (PyUnicode_CheckExact(lhs)) {
+                if (PyUnicode_CheckExact(lhs) && PyUnicode_IS_COMPACT_ASCII(lhs)) {
                     specialize(instr, BINARY_OP_SUBSCR_STR_INT);
                     return;
                 }