Optimize slice_iter.copied().next_chunk()
#103166
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r? @m-ou-se (rust-highfive has picked a reviewer for you, use r? to override) |
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Just my two cents, use |
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slice_iter.copied.next_chunkslice_iter.copied().next_chunk()
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@bors r=m-ou-se rollup |
bors
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Oct 19, 2022
…iaskrgr Rollup of 4 pull requests Successful merges: - rust-lang#103166 (Optimize `slice_iter.copied().next_chunk()`) - rust-lang#103176 (Fix `TyKind::is_simple_path`) - rust-lang#103178 (Partially fix `src/test/run-make/coverage-reports` when cross-compiling) - rust-lang#103198 (Update cargo) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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…imulacrum Specialize `iter::ArrayChunks::fold` for TrustedRandomAccess iterators ``` OLD: test iter::bench_trusted_random_access_chunks ... bench: 368 ns/iter (+/- 4) NEW: test iter::bench_trusted_random_access_chunks ... bench: 30 ns/iter (+/- 0) ``` The resulting assembly is similar to rust-lang#103166 but the specialization kicks in under different (partially overlapping) conditions compared to that PR. They're complementary. In principle a TRA-based specialization could be applied to all `ArrayChunks` methods, including `next()` as we do for `Zip` but that would have all the same hazards as the Zip specialization. Only doing it for `fold` is far less hazardous. The downside is that it only helps with internal, exhaustive iteration. I.e. `for _ in` or `try_fold` will not benefit. Note that the regular, `try_fold`-based and the specialized `fold()` impl have observably slightly different behavior. Namely the specialized variant does not fetch the remainder elements from the underlying iterator. We do have a few other places in the standard library where beyond-the-end-of-iteration side-effects are being elided under some circumstances but not others. Inspired by https://old.reddit.com/r/rust/comments/yaft60/zerocost_iterator_abstractionsnot_so_zerocost/
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The default
next_chunkimplementation suffers from having to assemble the array byte by byte vianext(), checking theOption<&T>and then dereferencing&T. The specialization copies the chunk directly from the slice.