gh-126204: Add a sys._jit_enabled helper

[Eclips4]

• Issue: Add a Py_JIT_ENABLED variable to pyconfig.h #126204

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📚 Documentation preview 📚: https://cpython-previews--126247.org.readthedocs.build/

[zooba]

I'm not convinced that pyconfig.h is the right home for this - it seems like just pulling it from sysconfig is sufficient.

I'd rather not take the changes in the PC/PCbuild directories if we don't have to.

[Eclips4]

That's fun. Due to incorrect assumptions, where JIT is actually enabled or not, this hack is no longer needed. Just setting PYTHON_JIT=0 is enough here.

[picnixz]

A final nitpick. And a question: is there a lot of

_PyOptimizerObject*optimizer=_Py_GetOptimizer();
if (optimizer!=NULL) {
Py_DECREF(optimizer);
...
}

in the code? if so, we could perhaps have some function that checks if there is an optimizer.

EDIT: Since we are moving to removing the _PyOptimizer API, it's possible we don't need this.

[Eclips4]

A final nitpick. And a question: is there a lot of

_PyOptimizerObject*optimizer=_Py_GetOptimizer();
if (optimizer!=NULL) {
Py_DECREF(optimizer);
...
}

in the code? if so, we could perhaps have some function that checks if there is an optimizer.

EDIT: Since we are moving to removing the _PyOptimizer API, it's possible we don't need this.

In fact, there are only two uses of _Py_GetOptimizer. I'm not sure if we should remove this usage in this PR.

[Eclips4]

Superseded by #129194