@neonene
Thanks for the truly excellent investigation!
@Raymond and @Steve,
If I understood OP (neonene) properly, changing Py_DECREF to a macro won't get back the entire 7% lost performance in pyperformance. neonene's investigations suggest that the entire eval function is now too big for PGO on MSVC. Fixing Py_DECREF may get us a few %, but all the other hot functions in eval are likely not being inlined as well. Their suggested patch in https://bugs.python.org/msg401743 works, but IMO, _may_ slow down DISPATCH() _slightly_ since it seems to introduce another jump.
I suggest using their patch only for MSVC until we think of something better in 3.11. The additional jump may not matter after PGO (and it surely isn't a 7% slowdown :). WDYT?