gh-117578: Introduce _PyType_GetModuleByDef2 private function

[neonene]

_PyType_GetModuleByDefInPairs(provisional name: outdated) is a private function that takes two types, runs PyType_GetModuleByDef() twice, and finally raises an error if any.

• Issue: PyType_GetModuleByDef family for binary functions performance #117578

[encukou]

Please don't change the documented behaviour of PyType_GetModuleByDef. It should return the first match.
That said, if you have several different modules with the same def in a MRO, things are probably not going the way you wanted. The distinction between the first/last matching entry would make more sense if you want the base type itself, not its ht_module.

[neonene]

I can also revert the starting value of the loop from 1 to 0, if you prefer. I've seen a slight performance change there, which may be negligible.

[encukou]

LGTM, thank you!
As for tests, this should be covered by the decimal test suite, but if you want to write a GetModuleByDef test please ping me for a review.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 RHEL7 LTO + PGO 3.x has failed when building commit 2c45148.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/96/builds/7358) and take a look at the build logs.
4. Check if the failure is related to this commit (2c45148) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/96/builds/7358

Failed tests:

• test_capi

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 10, done. remote: Counting objects: 10% (1/10) remote: Counting objects: 20% (2/10) remote: Counting objects: 30% (3/10) remote: Counting objects: 40% (4/10) remote: Counting objects: 50% (5/10) remote: Counting objects: 60% (6/10) remote: Counting objects: 70% (7/10) remote: Counting objects: 80% (8/10) remote: Counting objects: 90% (9/10) remote: Counting objects: 100% (10/10) remote: Counting objects: 100% (10/10), done. remote: Compressing objects: 11% (1/9) remote: Compressing objects: 22% (2/9) remote: Compressing objects: 33% (3/9) remote: Compressing objects: 44% (4/9) remote: Compressing objects: 55% (5/9) remote: Compressing objects: 66% (6/9) remote: Compressing objects: 77% (7/9) remote: Compressing objects: 88% (8/9) remote: Compressing objects: 100% (9/9) remote: Compressing objects: 100% (9/9), done. remote: Total 10 (delta 1), reused 3 (delta 1), pack-reused 0 
From https://github.com/python/cpython
* branch main -> FETCH_HEAD
Note: checking out '2c451489122d539080c8d674b391dedc1dedcb53'.
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git checkout -b new_branch_name
HEAD is now at 2c45148... gh-117578: Introduce _PyType_GetModuleByDef2 private function (GH-117661)
Switched to and reset branch 'main'
find: ‘build’: No such file or directoryfind: ‘build’: No such file or directoryfind: ‘build’: No such file or directoryfind: ‘build’: No such file or directorymake[2]: [Makefile:3101: clean-retain-profile] Error 1 (ignored)make: *** [Makefile:2232: buildbottest] Error 2

[mdboom]

@neonene: We should have measured the performance impact of this at the time, but it came up recently in conversation with @markshannon, so I decided to measure it.

While overall on the benchmarking suite it's kind of inconclusive (1% faster, which is below the usual noise threshold), for the one benchmark that uses _PyType_GetModuleByDef heavily (via that fraction extension), it saw a 5% improvement, as well as a 3% decrease in memory usage. Results here.