[jira] [Created] (ARROW-10990) [Rust]: SIMD implementation of compare kernels reads out of bounds

["Jörn Horstmann (Jira)" <ji...@apache.org>]

Jörn Horstmann created ARROW-10990:
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             Summary: [Rust]: SIMD implementation of compare kernels reads out of bounds
                 Key: ARROW-10990
                 URL: https://issues.apache.org/jira/browse/ARROW-10990
             Project: Apache Arrow
          Issue Type: Bug
          Components: Rust
            Reporter: Jörn Horstmann


The simd compare kernels use the following pattern to handle the remainder that is not a multiple of the number of vector lanes:

{code}
    if rem > 0 {
        let simd_left = T::load(left.value_slice(len - rem, lanes));
        let simd_right = T::load(right.value_slice(len - rem, lanes));
        let simd_result = op(simd_left, simd_right);
        let rem_buffer_size = (rem as f32 / 8f32).ceil() as usize;
        T::bitmask(&simd_result, |b| {
            result.extend_from_slice(&b[0..rem_buffer_size]);
        });
    }
{code}

While this avoids writing into result out of bounds, it still reads from the {{left}} and {{right}} arrays at out of bounds indices and valgrind complains about that. I propose to rewrite the logic to use chunked iteration, with a scalar loop for the remainder, similar to the change for arithmetic kernels in ARROW-10914.



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