Python/ceval.c (part 51)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers LOAD_GLOBAL specializations. See python_ceval50_detail for FOR_ITER specializations.

Map

Lines	Symbol	Role
1-80	LOAD_GLOBAL_MODULE	Load a name from the module's __dict__
81-160	LOAD_GLOBAL_BUILTIN	Load a builtin with version-checked cache
161-260	LOAD_GLOBAL (generic)	Fallback: module dict then builtins
261-360	Cache invalidation	Module dict version tag
361-500	STORE_GLOBAL / DELETE_GLOBAL	Write and delete module-level names

Reading

LOAD_GLOBAL_MODULE

// CPython: Python/ceval.c:4360 LOAD_GLOBAL_MODULE
inst(LOAD_GLOBAL_MODULE, (unused/4 -- null if (oparg & 1), res)) {
    /* Cache: (globals_version, index) */
    PyDictObject *dict = (PyDictObject *)GLOBALS();
    DEOPT_IF(!PyDict_CheckExact(dict));
    PyDictKeysObject *keys = dict->ma_keys;
    DEOPT_IF(cache->version != keys->dk_version);
    /* Direct index lookup using cached position */
    PyObject *res = _PyDictValues_GetItemByIndex(dict->ma_values, cache->index);
    DEOPT_IF(res == NULL);
    Py_INCREF(res);
    DISPATCH();
}

LOAD_GLOBAL_MODULE caches the index into the module dict's values array. Valid as long as dk_version matches. This avoids a hash lookup on every global variable access in a hot loop.

LOAD_GLOBAL_BUILTIN

// CPython: Python/ceval.c:4420 LOAD_GLOBAL_BUILTIN
inst(LOAD_GLOBAL_BUILTIN, (unused/4 -- null if (oparg & 1), res)) {
    /* Cache: (builtins_version, globals_version, index) */
    DEOPT_IF(cache->builtins_version != builtins_dict->ma_version_tag);
    DEOPT_IF(cache->globals_version != globals_dict->ma_version_tag);
    /* Direct lookup in builtins dict */
    PyObject *res = _PyDictValues_GetItemByIndex(builtins_dict->ma_values, cache->index);
    DEOPT_IF(res == NULL);
    Py_INCREF(res);
    DISPATCH();
}

The globals version check is important: if any global with the same name as the builtin is defined, the specialization deoptimizes. This allows len = my_len to shadow the builtin correctly.

Generic LOAD_GLOBAL

// CPython: Python/ceval.c:4480 LOAD_GLOBAL
inst(LOAD_GLOBAL, (unused/4 -- null if (oparg & 1), res)) {
    PyObject *name = GETITEM(FRAME_CO_NAMES, oparg >> 1);
    /* Check module dict first */
    res = PyDict_GetItemWithError(GLOBALS(), name);
    if (res != NULL) { Py_INCREF(res); DISPATCH(); }
    /* Then builtins */
    res = PyDict_GetItemWithError(BUILTINS(), name);
    if (res != NULL) { Py_INCREF(res); DISPATCH(); }
    PyErr_Format(PyExc_NameError, "name '%.200s' is not defined", ...);
    ERROR_IF(true, error);
}

The fallback always checks globals then builtins. No specialization cache is consulted.

gopy notes

LOAD_GLOBAL_MODULE checks objects.Dict.Version against a cached value and reads from a cached index. LOAD_GLOBAL_BUILTIN checks both the module dict version (to detect shadowing) and the builtins dict version. Both are in vm/eval_simple.go. STORE_GLOBAL calls objects.DictSetItem(frame.Globals, name, value).