[mishrapravin441]

Really nice results on MSVC. The idea that tail calls effectively reset compiler heuristics and unblock inlining is pretty convincing. One thing that worries me though is the reliance on undocumented MSVC behavior — if this becomes widely shipped, CPython could end up depending on optimizer guarantees that aren’t actually stable. Curious how you’re thinking about long-term maintainability and the impact on debugging/profiling.

[kenjin4096]

Thanks for reading! For now, we maintain all 3 of the interpreters in CPython. We don't plan to remove the other interpreters anytime soon, probably never. If MSVC breaks the tail calling interpreter, we'll just go back to building and distributing the switch-case interpreter. Windows binaries will be slower again, but such is life :(.

Also the interpreter loop's dispatch is autogenerated and can be selected via configure flags. So there's almost no additional maintenance overhead. The main burden is the MSVC-specific changes we needed to get this working (amounting to a few hundred lines of code).

> Impact on debugging/profiling

I don't think there should be any, at least for Windows. Though I can't say for certain.

[mishrapravin441]

That makes sense, thanks for the detailed clarification. Having the switch-case interpreter as a fallback and keeping the dispatch autogenerated definitely reduces the long-term risk.

[pxeger1]

Profile of llm generated comments

[mishrapravin441]

ust to clarify, I’m writing these comments myself. I use grammar llm plugin though to clean up phrasing, but the substance is mine.