gh-152785: Upgrade LLVM to LLVM 21 in GitHub Action

[vstinner]

Upgrade LLVM to LLVM 21 in GitHub Action jobs:

• Reusable Sanitizer
• Reusable Ubuntu ("Install Clang and BOLT")

• Issue: GitHub Action: upgrade LLVM, GCC, Java and Ubuntu #152785

[vstinner]

All jobs completed successfully.

@corona10@Fidget-Spinner: What do you think of upgrading to LLVM 22? Is there a reason to not use a newer LLVM version?

[corona10]

For BOLT, LGTM

[corona10]

But why not keep same version as JIT? In anycase I prefer unifying LLVM version as possible.

[vstinner]

But why not keep same version as JIT? In anycase I prefer unifying LLVM version as possible.

Tools/jit/_llvm.py looks for LLVM 21. If I understood correctly, it requires exactly this LLVM version. Correct me if I'm wrong.

[corona10]

Tools/jit/_llvm.py looks for LLVM 21. If I understood correctly, it requires exactly this LLVM version. Correct me if I'm wrong.

I mean why we need to upgrade to LLVM22, just upgrade to 21

[vstinner]

Well, usually a newer compiler is faster to build C code, produces faster programs, and provides better analysis of the code. So to me, it sounds interesting to use LLVM 22 instead of LLVM 21.

It would be nice if the JIT compiler would support LLVM 21 and LLVM 22, but it doesn't seem to be the case now.

For the JIT compiler, LLVM is only used to generate JIT stencils. For other CI jobs, LLVM is used to build the whole Python code base.

[vstinner]

@corona10: Are you ok with switching to LLVM 22? Or do you prefer to use LLVM 21 in all CI jobs? You approved the PR but then asked a question, so I'm now confused.

[corona10]

Prefer to keep it as 21 to match with JIT as possible.

[vstinner]

Ok, I updated the PR to use LLVM 21 instead.

[hugovk]

How far can we backport this? We need to keep the CI running until branch EOL, and it's easier to maintain if the branches are more similar to each other.

[miss-islington-app]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[bedevere-app]

GH-152968 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-152969 is a backport of this pull request to the 3.14 branch.

[vstinner]

How far can we backport this? We need to keep the CI running until branch EOL, and it's easier to maintain if the branches are more similar to each other.

I backported the change to the 3.15 branch.

@corona10 prefers to use the same LLVM version than the one used by the JIT compiler. But in the 3.14 branch, Tools/jit/_llvm.py requires LLVM 19. So I don't think that this change should be backported to 3.13 and 3.14 branches. At least, not now.

Note: In the 3.13 branch, Tools/jit/_llvm.py requires LLVM 18.