bpo-46541: Replace core use of _Py_IDENTIFIER() with statically initialized global objects. (gh-30928)

We're no longer using _Py_IDENTIFIER() (or _Py_static_string()) in any core CPython code.  It is still used in a number of non-builtin stdlib modules.

The replacement is: PyUnicodeObject (not pointer) fields under _PyRuntimeState, statically initialized as part of _PyRuntime.  A new _Py_GET_GLOBAL_IDENTIFIER() macro facilitates lookup of the fields (along with _Py_GET_GLOBAL_STRING() for non-identifier strings).

https://bugs.python.org/issue46541#msg411799 explains the rationale for this change.

The core of the change is in:

* (new) Include/internal/pycore_global_strings.h - the declarations for the global strings, along with the macros
* Include/internal/pycore_runtime_init.h - added the static initializers for the global strings
* Include/internal/pycore_global_objects.h - where the struct in pycore_global_strings.h is hooked into _PyRuntimeState
* Tools/scripts/generate_global_objects.py - added generation of the global string declarations and static initializers

I've also added a --check flag to generate_global_objects.py (along with make check-global-objects) to check for unused global strings.  That check is added to the PR CI config.

The remainder of this change updates the core code to use _Py_GET_GLOBAL_IDENTIFIER() instead of _Py_IDENTIFIER() and the related _Py*Id functions (likewise for _Py_GET_GLOBAL_STRING() instead of _Py_static_string()).  This includes adding a few functions where there wasn't already an alternative to _Py*Id(), replacing the _Py_Identifier * parameter with PyObject *.

The following are not changed (yet):

* stop using _Py_IDENTIFIER() in the stdlib modules
* (maybe) get rid of _Py_IDENTIFIER(), etc. entirely -- this may not be doable as at least one package on PyPI using this (private) API
* (maybe) intern the strings during runtime init

https://bugs.python.org/issue46541

1 files changed, 7 insertions, 15 deletions

diff --git a/Python/specialize.c b/Python/specialize.c
index b95bdf7..2175923 100644
--- a/Python/specialize.c
+++ b/Python/specialize.c
@@ -1,6 +1,7 @@
 #include "Python.h"
 #include "pycore_code.h"
 #include "pycore_dict.h"
+#include "pycore_global_strings.h"  // _Py_ID()
 #include "pycore_long.h"
 #include "pycore_moduleobject.h"
 #include "pycore_object.h"
@@ -596,8 +597,6 @@ specialize_module_load_attr(
 {
     PyModuleObject *m = (PyModuleObject *)owner;
     PyObject *value = NULL;
-    PyObject *getattr;
-    _Py_IDENTIFIER(__getattr__);
     assert((owner->ob_type->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0);
     PyDictObject *dict = (PyDictObject *)m->md_dict;
     if (dict == NULL) {
@@ -608,13 +607,8 @@ specialize_module_load_attr(
         SPECIALIZATION_FAIL(opcode, SPEC_FAIL_NON_STRING_OR_SPLIT);
         return -1;
     }
-    getattr = _PyUnicode_FromId(&PyId___getattr__); /* borrowed */
-    if (getattr == NULL) {
-        SPECIALIZATION_FAIL(opcode, SPEC_FAIL_OVERRIDDEN);
-        PyErr_Clear();
-        return -1;
-    }
-    Py_ssize_t index = _PyDict_GetItemHint(dict, getattr, -1,  &value);
+    Py_ssize_t index = _PyDict_GetItemHint(dict, &_Py_ID(__getattr__), -1,
+                                           &value);
     assert(index != DKIX_ERROR);
     if (index != DKIX_EMPTY) {
         SPECIALIZATION_FAIL(opcode, SPEC_FAIL_MODULE_ATTR_NOT_FOUND);
@@ -1223,7 +1217,6 @@ binary_subscr_fail_kind(PyTypeObject *container_type, PyObject *sub)
 }
 #endif
 
-_Py_IDENTIFIER(__getitem__);
 
 #define SIMPLE_FUNCTION 0
 
@@ -1268,7 +1261,7 @@ _Py_Specialize_BinarySubscr(
         goto success;
     }
     PyTypeObject *cls = Py_TYPE(container);
-    PyObject *descriptor = _PyType_LookupId(cls, &PyId___getitem__);
+    PyObject *descriptor = _PyType_Lookup(cls, &_Py_ID(__getitem__));
     if (descriptor && Py_TYPE(descriptor) == &PyFunction_Type) {
         PyFunctionObject *func = (PyFunctionObject *)descriptor;
         PyCodeObject *code = (PyCodeObject *)func->func_code;
@@ -1385,8 +1378,7 @@ _Py_Specialize_StoreSubscr(PyObject *container, PyObject *sub, _Py_CODEUNIT *ins
         }
         goto fail;
     }
-    _Py_IDENTIFIER(__setitem__);
-    PyObject *descriptor = _PyType_LookupId(container_type, &PyId___setitem__);
+    PyObject *descriptor = _PyType_Lookup(container_type, &_Py_ID(__setitem__));
     if (descriptor && Py_TYPE(descriptor) == &PyFunction_Type) {
         PyFunctionObject *func = (PyFunctionObject *)descriptor;
         PyCodeObject *code = (PyCodeObject *)func->func_code;
@@ -1474,7 +1466,6 @@ builtin_call_fail_kind(int ml_flags)
 #endif
 
 static PyMethodDescrObject *_list_append = NULL;
-_Py_IDENTIFIER(append);
 
 static int
 specialize_method_descriptor(
@@ -1486,7 +1477,8 @@ specialize_method_descriptor(
         return -1;
     }
     if (_list_append == NULL) {
-        _list_append = (PyMethodDescrObject *)_PyType_LookupId(&PyList_Type, &PyId_append);
+        _list_append = (PyMethodDescrObject *)_PyType_Lookup(&PyList_Type,
+                                                             &_Py_ID(append));
     }
     assert(_list_append != NULL);
     if (nargs == 2 && descr == _list_append) {