[llvm] [GISel] Funnel shift combiner port from SelectionDAG ISel to GlobalISel (PR #135132)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

> @mshockwave it's been a while (I personally got busy), but I'm still interested in getting this merged. It's basically ready (beyond needing to rebase to the most recent commits of course), I just need some input on the vector tests another reviewer mentioned. The original SelectionDAG ISel version of this didn't have any, and the RISCV backend of GlobalISel is making it tricky to write vector tests. Do I even need them here? If so, can you read my previous comment and let me know how I should proceed? I want to thank you again for taking the time to help me get involved in the LLVM codebase.

Oh nice! I'm glad you're still keen to work on this. Sorry I saw your previous comment but I was pretty occupied back then.
GISel's support on scalable vectors is indeed not as robust as its fixed vector counterpart. And RISCV is only able to translate a small set of instructions with scalable vectors. Switching to fixed vectors does help a lot either, because there appears to be some lacking legalizations on instructions with fixed vectors in RISCV's GISel backend.

So personally I think you could go ahead with only the scalar tests. Please rebase your PR and I'll give another round of review tomorrow morning.

Thanks again for pushing this forward!

https://github.com/llvm/llvm-project/pull/135132