slice/ascii: Optimize eq_ignore_ascii_case with auto-vectorization
#147436
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Refactor the current functionality into a helper function Use `as_chunks` to encourage auto-vectorization in the optimized chunk processing function Add a codegen test Add benches for `eq_ignore_ascii_case` The optimized function is initially only enabled for x86_64 which has `sse2` as part of its baseline, but none of the code is platform specific. Other platforms with SIMD instructions may also benefit from this implementation. Performance improvements only manifest for slices of 16 bytes or longer, so the optimized path is gated behind a length check for greater than or equal to 16.
rustbot
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Refactor the eq check into an inner function for reuse in tail checking Rather than fall back to the simple implementation for tail handling, load the last 16 bytes to take advantage of vectorization. This doesn't seem to negatively impact check time even when the remainder count is low.
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I've pushed a commit to avoid falling back to the scalar checking for the remainder handling. We reload the last 16 bytes of the slices if there's a remainder, which improves the 31 byte case and doesn't seem to regress the 17 byte case. |
the8472
reviewed
Oct 7, 2025
jhorstmann
reviewed
Oct 8, 2025
| let (other_chunks, _) = other.as_chunks::<N>(); | ||
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| // Branchless check to encourage auto-vectorization | ||
| const fn eq_ignore_ascii_inner(lhs: &[u8; N], rhs: &[u8; N]) -> bool { |
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When I copied this code into compiler explorer with -C opt_level=3, the call to eq_ignore_ascii_inner did not get inlined. I would suggest to mark this function #[inline(always)] and add a CHECK-NOT: call in the codegen test.
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I added the annotation and filecheck adaptation in a5ba248
Add #[inline(always)] to inner function and check not for filecheck test
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as_chunksto encourage auto-vectorization in the optimized chunk processing functioneq_ignore_ascii_caseThe optimized function is initially only enabled for x86_64 which has
sse2as part of its baseline, but none of the code is platform specific. Other platforms with SIMD instructions may also benefit from this implementation.Performance improvements only manifest for slices of 16 bytes or longer, so the optimized path is gated behind a length check for greater than or equal to 16.
Benchmarks - Cases below 16 bytes are unaffected, cases above all show sizeable improvements.