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Enable outline-atomics by default on aarch64 platforms without LSE #150455

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Enable outline-atomics by default on aarch64 platforms without LSE#150455
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yash-rana0101
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A-target-featureArea: Enabling/disabling target features like AVX, Neon, etc.C-enhancementCategory: An issue proposing an enhancement or a PR with one.E-help-wantedCall for participation: Help is requested to fix this issue.E-mediumCall for participation: Medium difficulty. Experience needed to fix: Intermediate.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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@tgross35
tgross35
opened on Dec 28, 2025

Since #144938 and #149633, most Aarch64 platforms that don't have LSE in the baseline enable the +outline-atomics target feature. We keep getting more targets that fall into this boat, however, so it's probably worth making this the default.

I think we can probably just unconditionally enable outline-atomics on all aarch64 targets without checking LSE, since LLVM should ignore it if +lse is also set/implied.

Note that Apple targets would need an explicit disable until #149634 is fixed.

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  1. tgross35
    added
    C-enhancementCategory: An issue proposing an enhancement or a PR with one.
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    E-help-wantedCall for participation: Help is requested to fix this issue.
    E-mediumCall for participation: Medium difficulty. Experience needed to fix: Intermediate.
    A-target-featureArea: Enabling/disabling target features like AVX, Neon, etc.
    on Dec 28, 2025
  2. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Dec 28, 2025
  3. tgross35
    removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Dec 28, 2025

  4. JayanAXHF commented on Jan 27, 2026

    @JayanAXHF
    JayanAXHF
    on Jan 27, 2026
    Member

    Is this still unimplemented?

  5. tgross35 commented on Jan 28, 2026

    @tgross35
    tgross35
    on Jan 28, 2026
    MemberAuthor

    Yeah, it's still available. Note that we can't land it immediately because there is currently a problem with our outline atomics in compiler-builtins, but that should be resolved in the near future.

  6. yash-rana0101 commented on Feb 20, 2026

    @yash-rana0101
    yash-rana0101
    on Feb 20, 2026

    @rustbot claim

  7. rustbot
    assigned
    yash-rana0101
    on Feb 20, 2026
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A-target-featureArea: Enabling/disabling target features like AVX, Neon, etc.C-enhancementCategory: An issue proposing an enhancement or a PR with one.E-help-wantedCall for participation: Help is requested to fix this issue.E-mediumCall for participation: Medium difficulty. Experience needed to fix: Intermediate.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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