Hm, it doesn't sound right to override profile-guided optimization, especially sincetest_decimal (the only current caller of_PyType_GetModuleByDef2) is in the PGO test set.
Does this PR have a significant performance impact?

It is mentioned onthe faster-cpython repo that thetelco test has slowed down a lot.

According to MSVC, the module state access counts were:

Function / breakdown     entry-cnt  alternative access-----------------------  ---------  ---------------------------PyType_GetModuleByDef()    6852643    convert_op             2971848  via context object    PyDecType_New          1651188  via context object (partial)    dec_addstatus          1651188  via context object (partial)    current_context        1486221  via context object (partial)    dec_mpd_qquantize       247731  METH_METHOD    ctx_mpd_qquantize       165000  METH_METHOD    ..._PyType_GetModuleByDef2()  1073193    nm_mpd_qadd             660462    nm_mpd_qmul             412731

Tested with the/Ob3 option, switching the inlining specifier:f740a5d. My Release/PGO builds on Windows get slower using TLS version ofPyThreadState_Get(), which is also observed at#103324 (comment). If *nix OSes are in good health with TLS, I guess I also need to run thetelco with a good condition (without TLS):

This patch would need to be applied if we wanted as much speed as the global state access on Windows, which has little effect alone (1%) for some reason.

Windows PGO:
- telco: 9.21 ms +- 0.12 ms -> 9.02 ms +- 0.09 ms: 1.02x faster

Is it acceptable thattest_decimal.py has a test case like below, instead of touching the C code?

@requires_cdecimalclassCArithmeticOperatorsTest(ArithmeticOperatorsTest,unittest.TestCase):    ...@unittest.skipIf(nottest.support.PGO,'PGO training only')deftest_excecise_binop(self):Decimal=self.decimal.Decimald=Decimal('11.1')foriinrange(500000):1+d# at least 300000 times

I'll tryPyType_GetBaseByToken() version.

Closing in favor of proposing thePyType_GetBaseByToken() version, which can supersede_PyType_GetModuleByDef2() on PGO and Relase(/Ob3) builds.