[llvm] [LV] Add support for partial reductions without a binary op (PR #133922)

[David Sherwood via llvm-commits]

david-arm wrote:

If both of those PRs are close to landing I could try to check them out and see how my PR interacts with them, but I'd rather do that once I know they're clos(ish) to the finish line.

https://github.com/llvm/llvm-project/pull/133922