Faster take with null values (2-3x)

[jorgecarleitao]

This was achieved by splitting the "take" of values and validity as two separate loops. It seems to vectorize better.

# native = skylake-avx512
RUSTFLAGS="-C target-cpu=native" cargo bench --features compute,benchmarks \
    --bench take_kernels -- "take .* values nulls 2\^20"

take i32 values nulls 2^20                                                                            
                        time:   [6.2657 ms 6.2879 ms 6.3151 ms]
                        change: [-57.959% -57.507% -57.123%] (p = 0.00 < 0.05)
take bool values nulls 2^20                                                                             
                        time:   [4.4977 ms 4.5077 ms 4.5197 ms]
                        change: [-69.940% -69.411% -68.964%] (p = 0.00 < 0.05)
take str values nulls 2^20                                                                            
                        time:   [25.706 ms 25.878 ms 26.063 ms]
                        change: [-20.546% -19.827% -19.031%] (p = 0.00 < 0.05)

This was a side observation of DataEngineeringLabs/simd-benches#1 which showed that

pub fn naive_take(values: &[f32], indices: &[usize]) -> Vec<f32> {
    indices.iter().map(|i| values[*i]).collect()
}

is compiled to the same instructions as using portable_simd's gather, suggesting that the compiler is quite smart in compiling naive_take and we can thus leverage that.

[ritchie46]

Intersting. I also had a similar result with splitting the bound check in two loops.

Maybe that makes sense here as well. Als it is now checked in the validity and in the values.

[codecov]

Codecov Report

Merging #633 (865ad04) into main (e9a6c3e) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #633      +/-   ##
==========================================
- Coverage   69.92%   69.91%   -0.02%     
==========================================
  Files         300      300              
  Lines       16634    16627       -7     
==========================================
- Hits        11632    11625       -7     
  Misses       5002     5002              

Impacted Files	Coverage Δ
src/compute/take/boolean.rs	90.00% <100.00%> (-0.39%)	⬇️
src/compute/take/generic_binary.rs	97.70% <100.00%> (-0.06%)	⬇️
src/compute/take/primitive.rs	89.58% <100.00%> (-0.62%)	⬇️
src/compute/arithmetics/time.rs	42.30% <0.00%> (-1.93%)	⬇️
src/bitmap/utils/slice_iterator.rs	92.53% <0.00%> (+1.49%)	⬆️

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[Dandandan]

Cool results 😎