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GH-139922: Tail calling for MSVC (VS 2026)#143068

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Fidget-Spinner merged 11 commits into
python:mainfrom
chris-eibl:msvc-tail-call-new
Dec 22, 2025
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GH-139922: Tail calling for MSVC (VS 2026)#143068
Fidget-Spinner merged 11 commits into
python:mainfrom
chris-eibl:msvc-tail-call-new

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@chris-eibl

@chris-eibl chris-eibl commented Dec 22, 2025 •
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So much has happened on main that I started fresh over and sqash merged the needed things from #139962 onto latest main (mostly because I wanted to use it for my own experiments on main again).

Based on @markshannon's work in #142228 I've factored out _Py_VectorCallInstrumentation_StackRefSteal, because then @Fidget-Spinner's #138115 is not needed in this PR and can be done in a follow-up. An alternative would be to keep it and pass tstate into the Py_*_StackRefSteal functions.

@bedevere-app bedevere-app Bot mentioned this pull request Dec 22, 2025
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@chris-eibl chris-eibl marked this pull request as ready for review December 22, 2025 14:23
@Fidget-Spinner

Fidget-Spinner commented Dec 22, 2025

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In the future, please communicate if you want to supercede a PR for other contributors. It's often considered not good etiquette to take over another person's PR unless they explicitly allow it. However, I'm more than happy to let you take over the PR in this case.

@chris-eibl

chris-eibl commented Dec 22, 2025

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In the future, please communicate if you want to supercede a PR for other contributors. It's often considered not good etiquette to take over another person's PR unless they explicitly allow it. However, I'm more than happy to let you take over the PR in this case.

Sorry, wasn't ment as superseding, more as a follow up and maybe just a draft for new discussions. Thought about you're gonna take whatever deems appropriate back into your original PR ...

If this here is going to fly, I'd like to include you and Brandt as authors for the commits, but don't know how atm ...

@hugovk

hugovk commented Dec 22, 2025

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If this here is going to fly, I'd like to include you and Brandt as authors for the commits, but don't know how atm ...

Co-authored-by is the way:

https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors

@Fidget-Spinner

Fidget-Spinner commented Dec 22, 2025

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If this here is going to fly, I'd like to include you and Brandt as authors for the commits, but don't know how atm ...

Oh I'm happy to be superseded. If you'd like to attribute commit history though, you can just push a trivial commit with the co-author info like Hugo pointed out, and when I squash and merge I'll use that.

@chris-eibl @Fidget-Spinner @brandtbucher
make _PyMapping_GetOptionalItem2 private and comment scopes …
fdfd8a0 
Co-Authored-By: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
Co-Authored-By: Brandt Bucher <brandt@python.org>
@Fidget-Spinner

Fidget-Spinner commented Dec 22, 2025

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Try pulling main in, I fixed a JIT bug there that should turn the JIT CI green again.

@chris-eibl

chris-eibl commented Dec 22, 2025

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Co-authored-by is the way:

Done

chris-eibl and others added 2 commits December 22, 2025 17:44
@chris-eibl @hugovk
Apply suggestions from code review …
c8d051b 
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
@chris-eibl @hugovk
Update .github/workflows/tail-call.yml …
ab70524 
I could not add this one to batch, so have to do it separately

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
@chris-eibl

chris-eibl commented Dec 22, 2025

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https://github.com/python/cpython/actions/runs/20437258430/job/58722460806 failed inbetween
test_extractall_none_gid (test.test_tarfile.NoneInfoExtractTests_Tar.test_extractall_none_gid) ... Windows fatal exception: access violation
(but got green when rerunning the failed test) even though pulling in main.

I've found this: #143073

Hopefully, this will fix it ...

@chris-eibl
enable "Emulated Windows Clang (release)" …
5c1c240 
try to fix "Native Windows MSVC (release)"
@Fidget-Spinner

Fidget-Spinner commented Dec 22, 2025 •
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Just ignore the JIT problems for now. The new JIT executor management has a known bug #143026

@Fidget-Spinner Fidget-Spinner added the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label Dec 22, 2025
@bedevere-bot

bedevere-bot commented Dec 22, 2025

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🤖 New build scheduled with the buildbot fleet by @Fidget-Spinner for commit da1adaf 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F143068%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

@bedevere-bot bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label Dec 22, 2025
@Fidget-Spinner

Fidget-Spinner commented Dec 22, 2025 •
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Benchmark results are within noise for the default interpreter https://github.com/facebookexperimental/free-threading-benchmarking/blob/main/results/bm-20251222-3.15.0a3%2B-da1adaf/bm-20251222-vultr-x86_64-chris%252deibl-msvc_tail_call_new-3.15.0a3%2B-da1adaf-vs-base.md

Refleak bots are green.

Fidget-Spinner
Fidget-Spinner approved these changes Dec 22, 2025
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Once again:

  • This PR is the successor of one that has been up for 2 months already #139962 . We've had enough discussion there to get a sensing of what we want.
  • Refleak tests are green, performance results are within noise for the default (computed goto) interpreter.
  • This PR adds CI for the new configuration, which is also green.
  • I have discussed this feature with the other core devs a few months back on our bi-weekly perf meetings. Everyone was in agreement that adding scopes to MSVC is fine as it isn't that invasive.
  • This PR is the minimal changeset required to get TC working on MSVC.
  • It uses the techniques suggested by Mark in the other PR (just adding scopes and commenting on them). So I expect he should be okay with the overall design I hope. I understand he might disagree on some of the smaller changes.
  • It LGTM, from my review of the changes.

Therefore, I'm merging this PR.

Any follow-ups can be done on future PRs. Any discussion about the design can be done on the issue itself.

Hide details View details @Fidget-Spinner Fidget-Spinner merged commit be3c131 into python:main Dec 22, 2025
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@hugovk hugovk mentioned this pull request Dec 23, 2025
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@chris-eibl chris-eibl deleted the msvc-tail-call-new branch December 26, 2025 17:45
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@markshannon markshannon markshannon is a code owner

@ezio-melotti ezio-melotti Awaiting requested review from ezio-melotti

@AA-Turner AA-Turner Awaiting requested review from AA-Turner AA-Turner is a code owner

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