The LOAD_GLOBAL bytecode has a fast-path when globals and builtins have exactly the type 'dict'. It calls the _PyDict_LoadGlobal() function.

I propose to implement a similar optimization for LOAD_NAME, see attached patch.

The patch also fixes LOAD_GLOBAL and LOAD_NAME bytecodes when locals, globals or builtins are not exactly the type 'dict'. It clears the KeyError before trying the next PyObject_GetItem().

The patch changes also _PyDict_LoadGlobal() to call PyObject_Hash() if the hash was not computed yet. It might make it a little bit faster.

When LOAD_NAME is generated? Is it worth to optimize this case? Aren't LOAD_FAST and LOAD_GLOBAL used in performance critical code?

It looks to me that there is a bug in fast path of _PyDict_LoadGlobal. If the first lookup fails, it can raise an exception. We have to add

    if (PyErr_Occurred())
        return NULL;

before the second lookup.

Just for reference, the fast path for LOAD_GLOBAL was added in 8f8fe990e82c.

> When LOAD_NAME is generated? Is it worth to optimize this case? Aren't LOAD_FAST and LOAD_GLOBAL used in performance critical code?

I guess that it's only used to execute the body of modules.

> Is it worth to optimize this case?

Hum, I don't know :-)

> It looks to me that there is a bug in fast path of _PyDict_LoadGlobal. If the first lookup fails, it can raise an exception.

Sorry, where exactly? Can you maybe put a comment on the review? I see many checks to handle errors.

Rebased patch (ceval.c was modified by the changeset of c1414f80ebc9, issue #25556).

New changeset c35d65c9ded3 by Victor Stinner in branch 'default':
Issue #25557: Refactor _PyDict_LoadGlobal()
https://hg.python.org/cpython/rev/c35d65c9ded3

Since LOAD_NAME is rare, I don't think that it's worth to optimize it.

I pushed a partial version of pydict_loadname-2.patch to add comments to the code.

Thanks Victor.