INADA Naoki: "Maybe, we should do: * Make clinic use more METH_FASTCALL * Use clinic more in builtin methods; before trying this optimization."
I created the issue #29286 "Use METH_FASTCALL in str methods" which is now fixed. I started to propose patches for other funnctions, types and modules.
Would you mind to rebase your loadmethod-fastcall.patch patch Naoki?
With my change 0b219348ec9e, I'm not sure that your change on methoddescr_call() is still needed.
I tried to rebase your change, but I failed to get the "1.10x faster" result. Maybe I did something wrong, maybe my change 0b219348ec9e already optimized method calls for C functions?