Enables initial non-power-of-2 support (but still requires number of
elements, forming whole registers) for reductions.
Enables extra vectorization for
MultiSource/Benchmarks/7zip/7zip-benchmark, CINT2006/464.h264ref and
CFP2017rate/526.blender_r (checked for SSE2)
Reviewers: RKSimon
Reviewed By: RKSimon
Pull Request: https://github.com/llvm/llvm-project/pull/112361