gh-132657: Improve performance in specialize_dict_access_hint() via adding specialization for PY_GIL_DISABLED

Misc/NEWS.d/next/Core_and_Builtins/2026-02-16-18-23-13.gh-issue-132657.SeGcFx.rst

@@ -0,0 +1,2 @@
+In the free-threaded build, dictionary access hint specializations now attempt to enable deferred reference counting for resolved values owned by a different thread, reducing cross-thread reference count traffic and improving multi-threaded scalability.
+Patch by Benedikt Johannes.

Python/specialize.c

@@ -644,14 +644,22 @@ specialize_dict_access_hint(
         SPECIALIZATION_FAIL(base_op, SPEC_FAIL_ATTR_SPLIT_DICT);
         return 0;
     }
-    Py_ssize_t index = _PyDict_LookupIndex(dict, name);
+    PyObject *value;
+    Py_ssize_t index = _PyDict_LookupIndexAndValue(dict, name, &value);
+    if (value != NULL && PyLazyImport_CheckExact(value)) {
+        SPECIALIZATION_FAIL(base_op, SPEC_FAIL_ATTR_MODULE_LAZY_VALUE);
+        return 0;
+    }
     if (index != (uint16_t)index) {
         SPECIALIZATION_FAIL(base_op,
                             index == DKIX_EMPTY ?
                             SPEC_FAIL_ATTR_NOT_IN_DICT :
                             SPEC_FAIL_OUT_OF_RANGE);
         return 0;
     }
+#ifdef Py_GIL_DISABLED
+    maybe_enable_deferred_ref_count(value);
+#endif
     cache->index = (uint16_t)index;
     write_u32(cache->version, tp_version);
     specialize(instr, hint_op);