repr(transparent) check: do not compute check_unsuited more than once #148281
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r? @spastorino rustbot has assigned @spastorino. Use |
RalfJung
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Oct 30, 2025
| let layout = tcx.layout_of(typing_env.as_query_input(ty)); | ||
| // We are currently checking the type this field came from, so it must be local | ||
| let span = tcx.hir_span_if_local(field.did).unwrap(); | ||
| let trivial = layout.is_ok_and(|layout| layout.is_1zst()); |
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There is still some code here we are running twice, in particular the layout_of query. The alternative would be to simply collect the results into a Vec, which will cost us an allocation but then avoids running the iterator twice.
hkBst
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@rustbot reroll |
nnethercote
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Nov 18, 2025
| } | ||
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| FieldInfo { span, trivial, unsuited: check_unsuited(tcx, typing_env, ty).break_value() } | ||
| return FieldInfo { span, trivial, ty }; |
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| return FieldInfo { span, trivial, ty }; | |
| FieldInfo { span, trivial, ty } |
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r=me with the nit fixed. |
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This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed. Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers. |
spastorino
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@bors r=nnethercote rollup |
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Rollup of 5 pull requests Successful merges: - #147887 (Improve the documentation of atomic::fence) - #148281 (repr(transparent) check: do not compute check_unsuited more than once) - #148484 (Fix suggestion for the `cfg!` macro) - #149057 (`rust-analyzer` subtree update) - #149061 (debug-assert FixedSizeEncoding invariant) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup of 5 pull requests Successful merges: - #147887 (Improve the documentation of atomic::fence) - #148281 (repr(transparent) check: do not compute check_unsuited more than once) - #148484 (Fix suggestion for the `cfg!` macro) - #149057 (`rust-analyzer` subtree update) - #149061 (debug-assert FixedSizeEncoding invariant) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of #148281 - RalfJung:repr-transparent-check, r=nnethercote repr(transparent) check: do not compute check_unsuited more than once `field_infos` is an iterator that we execute multiple times. However, we usually ignore the `unsuited` field -- we only need it in the last iteration. So move the computation of that field to that iteration to avoid computing it multiple times. Computing `unsuited` involves a recursive traversal over the types of all non-trivial fields, so there can be non-trivial amounts of work here. (I benchmarked this in #148243 and saw no changes, probably because we don't have a benchmark with many repr(transparent) types. But still, computing this each time just seemed silly.)
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Rollup of 5 pull requests Successful merges: - rust-lang/rust#147887 (Improve the documentation of atomic::fence) - rust-lang/rust#148281 (repr(transparent) check: do not compute check_unsuited more than once) - rust-lang/rust#148484 (Fix suggestion for the `cfg!` macro) - rust-lang/rust#149057 (`rust-analyzer` subtree update) - rust-lang/rust#149061 (debug-assert FixedSizeEncoding invariant) r? `@ghost` `@rustbot` modify labels: rollup
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field_infosis an iterator that we execute multiple times. However, we usually ignore theunsuitedfield -- we only need it in the last iteration. So move the computation of that field to that iteration to avoid computing it multiple times. Computingunsuitedinvolves a recursive traversal over the types of all non-trivial fields, so there can be non-trivial amounts of work here.(I benchmarked this in #148243 and saw no changes, probably because we don't have a benchmark with many repr(transparent) types. But still, computing this each time just seemed silly.)