Switching to clang16

[a-turko]

Hi,

I was thinking about making Cling use a newer version of Clang (Clang 16) to improve support for C++20. I'm wondering what the complexity of this change would be.
Is this something you've looked into? What would be your estimate of the amount of work needed to do that?

[SimeonEhrig]

It's definitely which we are looking for. Unfortunately most of LLVM upgrades are a lot of work. This is the PR to upgrade from LLVM 9 to LLVM 13: root-project/root#10294

And we are still fixing bugs, to release an new Cling version with LLVM 13. But there is also a lot of ongoing work to solve this problem in future. Clang-repl was created to move a lot of cling related development on the llvm and clang components to the llvm upstream. This should make the cling source code smaller, which makes easier to upgrade to a new llvm version.

[a-turko]

Thanks @SimeonEhrig for the pointer to clang-repl. From what I read it seems that for use cases outside of High Energy Physics one could replace cling with clang-repl.
Can I assume that being a clang tool, clang-repl uses a JIT compiler that supports all C++ features supported by clang in the current version?

[SimeonEhrig]

Thanks @SimeonEhrig for the pointer to clang-repl. From what I read it seems that for use cases outside of High Energy Physics one could replace cling with clang-repl.

Yes, that is the goal of clang-repl.

Can I assume that being a clang tool, clang-repl uses a JIT compiler that supports all C++ features supported by clang in the current version?

There is not guaranty but a good chance that a lot of the C++ features are working. Unfortunately clang-repl introduces sometimes new "bugs", because it's works principal with the translation units and how the repl interface is working. I suggest to simply test it and open an issue if it does work. This would help us a lot of.

[BrainStone]

Hey :)

I saw that the MR root-project/root#10294 has been merged. Any updates on the state here?

[Axel-Naumann]

root-project/root#10294 is for llvm13 and from last year, so not related.

We have branched for ROOT's release, next is the llvm 16 upgrade in master. Afaik root-project/root#13815 is the only remaining issue; @hahnjo can state this with more authority.

[hahnjo]

just to post the link to the right PR for the upgrade to LLVM 16: root-project/root#13273

[hahnjo]

We merged the upgrade this morning! 🥳