[andv, eorv, orv, s/uaddv, s/umaxv, s/uminv]
sve_reduce_##(none, ?) -> op's neutral value
sve_reduce_##(any, neutral) -> op's neutral value
[andv, orv, s/umaxv, s/uminv]
sve_reduce_##(all, splat(X)) -> X
[eorv]
sve_reduce_##(all, splat(X)) -> 0