[llvm] [LoopUnroll] Introduce parallel reduction phis when unrolling. (PR #149470)

[Florian Hahn via llvm-commits]

fhahn wrote:

> I was imprecise when I said you "can't unroll" that loop; technically you can unroll almost anything. But your current version of reduction detection won't work for that loop, and making reduction detection work would require significant infrastructure changes to unrolling, to introduce runtime checks.

Ah sorry, the initial version of the patch was missing a check for reductions with intermediate stores, so it incorrectly introduced parallel reduction phis for the loop. Should be fixed in the latest version + test added, thanks

https://github.com/llvm/llvm-project/pull/149470