[llvm] [AArch64] Enable RT and partial unrolling with reductions for Apple CPUs. (PR #149699)

[Florian Hahn via llvm-commits]

fhahn wrote:

Updated the PR after landing https://github.com/llvm/llvm-project/pull/149470. Main change from previous version is adding a new `AddAdditionalAccumulators` TTI hook

https://github.com/llvm/llvm-project/pull/149699