Reduce vs. foldl: performance and precision

General Usage Performance
,
7

Oh, right. I was thinking of

function naivesum(a)
    s = zero(eltype(a))
    @simd for x in a
        s += x
    end
    return s
end

which is mostly left-to-right summation but is not strictly left-to-right at a fine-grained level because @simd allows some reassociation. This achieves basically the same performance as sum:

julia> @btime sum($a);
  5.047 ms (0 allocations: 0 bytes)

julia> @btime naivesum($a);
  5.166 ms (0 allocations: 0 bytes)
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