⏪️ [MLIR] Bring back MLIR / LLVM 19.0 support

[flowerthrower]

Description

Reincarnate MLIR / LLVM 19.0 support.
Necessary for Catalyst-related efforts (like #880).

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

📢 Thoughts on this report? Let us know!

[burgholzer]

Overall LGTM. Just some minor fixes necessary.

[burgholzer]

Probably also worth a changelog entry.

[flowerthrower]

Thanks @burgholzer for the quick review. I added the requested changes.
We currently only test with v20, which is an issue, as the behaviour of the transformation passes is (somehow) different in v19 and the CHECKs inside of Dialect/MQTOpt/Transforms/branch-opt.mlir and Dialect/MQTOpt/Transforms/branch-opt. mlir fail. @ystade was so kind to offer support in this regard.

[burgholzer]

Thanks @burgholzer for the quick review. I added the requested changes. We currently only test with v20, which is an issue, as the behaviour of the transformation passes is (somehow) different in v19 and the CHECKs inside of Dialect/MQTOpt/Transforms/branch-opt.mlir and Dialect/MQTOpt/Transforms/branch-opt. mlir fail. @ystade was so kind to offer support in this regard.

Sounds good to me! The current code changes all look reasonable.
What is still missing is re-enabling the CI on LLVM@19.
That should also surface the error you are talking about.
You should be able to simply revert the ci_mlir.yml file to a previous version that still tested for both versions.

[ystade]

We know that applyPatternsGreedilyAndFold(...) still exists in LLVM 20 but is deprecated. Assuming that this function has the identical behaviour in LLVM 19 and LLVM 20, in our use case, it should even be identical to the function applyPatternsGreedily(...) newly introduced in LLVM 20. The deprecated function applyPatternsGreedilyAndFold(...) in LLVM just sets the field config.fold = true and then calls applyPatternsGreedily(...). Since we are not specifying any particular config and the default value for the fold member is true, both function should have the same behaviour in the end.

[ystade]

Apparently, the latest minor version of LLVM 19 does not cause any issues in our tests, and this PR should be ready to go in. Is that correct, @burgholzer?

[flowerthrower]

Thank you @ystade! Looks like this is only an issue with the v19 that is used (and possibly patched) in Catalyst---the one I have been using on my local machine.

[burgholzer]

LGTM 👍🏼