[llvm] [LoopVectorizer] Add support for partial reductions (PR #92418)

[Sam Tebbs via llvm-commits]

SamTebbs33 wrote:

> I may have missed one, but it looks like none of the current tests actually emit the partial reduction intrinsic. Has something changed in the detection of dot-like instruction sequences?

You are correct actually. It wasn't producing the partial reductions since `isPartialReductionSupported` was returning false for all targets. I've now enabled it for AArch64 with SVE or Neon.

https://github.com/llvm/llvm-project/pull/92418