This is part of what is requested by PR42023:
https://bugs.llvm.org/show_bug.cgi?id=42023
There's an extension needed for FP add, but exactly how we would specify that using flags is not clear to me, so I left that as a TODO.
We're still missing patterns for partial reductions when the input vector is 256-bit or 512-bit, but I think that's a failure of vector narrowing. If we can reduce the widths, then this matching should work on those tests.
(style) early-out if this is not the case