Stabilize passing 128-bit integers via vector registers with `asm!` on x86 by folkertdev · Pull Request #159525 · rust-lang/rust

folkertdev · 2026-07-18T15:15:08Z

tracking issue: #133416
reference PR: rust-lang/reference#2313

Stabilization report

Summary

Stabilize passing 128-bit integers via vector registers with asm! on x86 and x86_64:

// Use 128-bit integers with vector registers.
let mut v = 0u128;

asm!("/* {:x} */", in(xmm_reg) v);
asm!("/* {:x} */", out(xmm_reg) v);

asm!("/* {:y} */", in(ymm_reg) v);
asm!("/* {:y} */", out(ymm_reg) v);

asm!("/* {:z} */", in(zmm_reg) v);
asm!("/* {:z} */", out(zmm_reg) v);

32-bit and 64-bit integer types can already be passed via vector registers. LLVM has supported 128-bit integers since 2019, see llvm/llvm-project#42502, so rustc not supporting them seems like an oversight.

This feature is part of asm_experimental_reg. We're not stabilizing that feature as a whole, but only pull out part of it.

History

x86: support passing u128/i128 to inline assembly #151059

Open questions

None.

r? Amanieu

…n x86

traviscross · 2026-07-22T14:55:50Z

Thanks @folkertdev.

@rfcbot fcp merge lang

rust-rfcbot · 2026-07-22T14:55:52Z

@traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

tmandry · 2026-07-22T15:28:53Z

@rfcbot reviewed

nikomatsakis · 2026-07-22T15:29:16Z

@rfcbot reviewed

rust-rfcbot · 2026-07-22T15:29:29Z

🔔 This is now entering its final comment period, as per the review above. 🔔

Amanieu

r=me once FCP completes

View changes since this review

rust-rfcbot · 2026-08-01T15:29:58Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

folkertdev · 2026-08-01T20:05:22Z

@bors r=Amanieu

rust-bors · 2026-08-01T20:05:26Z

📌 Commit b68b9bc has been approved by Amanieu

It is now in the queue for this repository.

… r=Amanieu Stabilize passing 128-bit integers via vector registers with `asm!` on x86 tracking issue: rust-lang#133416 reference PR: rust-lang/reference#2313 # Stabilization report ## Summary Stabilize passing 128-bit integers via vector registers with `asm!` on x86 and x86_64: ```rust // Use 128-bit integers with vector registers. let mut v = 0u128; asm!("/* {:x} */", in(xmm_reg) v); asm!("/* {:x} */", out(xmm_reg) v); asm!("/* {:y} */", in(ymm_reg) v); asm!("/* {:y} */", out(ymm_reg) v); asm!("/* {:z} */", in(zmm_reg) v); asm!("/* {:z} */", out(zmm_reg) v); ``` 32-bit and 64-bit integer types can already be passed via vector registers. LLVM has supported 128-bit integers since 2019, see llvm/llvm-project#42502, so `rustc` not supporting them seems like an oversight. This feature is part of [`asm_experimental_reg`](rust-lang#133416). We're not stabilizing that feature as a whole, but only pull out part of it. ## History - rust-lang#151059 ## Open questions None. r? Amanieu

Rollup of 6 pull requests Successful merges: - #159844 (Subtree cg_gcc sync (2026-07-24)) - #156527 (Move `std::io` tests to `alloctests` & add prelude) - #159525 (Stabilize passing 128-bit integers via vector registers with `asm!` on x86) - #160342 (Specialize `advance_by` method of `Fuse`) - #106643 (Allow only implementing `Read::read_buf`) - #159729 (allocations are allowed to grow (but not shrink))

… r=Amanieu Stabilize passing 128-bit integers via vector registers with `asm!` on x86 tracking issue: rust-lang#133416 reference PR: rust-lang/reference#2313 # Stabilization report ## Summary Stabilize passing 128-bit integers via vector registers with `asm!` on x86 and x86_64: ```rust // Use 128-bit integers with vector registers. let mut v = 0u128; asm!("/* {:x} */", in(xmm_reg) v); asm!("/* {:x} */", out(xmm_reg) v); asm!("/* {:y} */", in(ymm_reg) v); asm!("/* {:y} */", out(ymm_reg) v); asm!("/* {:z} */", in(zmm_reg) v); asm!("/* {:z} */", out(zmm_reg) v); ``` 32-bit and 64-bit integer types can already be passed via vector registers. LLVM has supported 128-bit integers since 2019, see llvm/llvm-project#42502, so `rustc` not supporting them seems like an oversight. This feature is part of [`asm_experimental_reg`](rust-lang#133416). We're not stabilizing that feature as a whole, but only pull out part of it. ## History - rust-lang#151059 ## Open questions None. r? Amanieu

Rollup of 6 pull requests Successful merges: - #156527 (Move `std::io` tests to `alloctests` & add prelude) - #159525 (Stabilize passing 128-bit integers via vector registers with `asm!` on x86) - #160342 (Specialize `advance_by` method of `Fuse`) - #106643 (Allow only implementing `Read::read_buf`) - #159729 (allocations are allowed to grow (but not shrink)) - #159881 (fix: Do not stop `visible_parent_map` breadth-first search reaching children of `#[doc(hidden)]` modules)

… r=Amanieu Stabilize passing 128-bit integers via vector registers with `asm!` on x86 tracking issue: rust-lang#133416 reference PR: rust-lang/reference#2313 # Stabilization report ## Summary Stabilize passing 128-bit integers via vector registers with `asm!` on x86 and x86_64: ```rust // Use 128-bit integers with vector registers. let mut v = 0u128; asm!("/* {:x} */", in(xmm_reg) v); asm!("/* {:x} */", out(xmm_reg) v); asm!("/* {:y} */", in(ymm_reg) v); asm!("/* {:y} */", out(ymm_reg) v); asm!("/* {:z} */", in(zmm_reg) v); asm!("/* {:z} */", out(zmm_reg) v); ``` 32-bit and 64-bit integer types can already be passed via vector registers. LLVM has supported 128-bit integers since 2019, see llvm/llvm-project#42502, so `rustc` not supporting them seems like an oversight. This feature is part of [`asm_experimental_reg`](rust-lang#133416). We're not stabilizing that feature as a whole, but only pull out part of it. ## History - rust-lang#151059 ## Open questions None. r? Amanieu

…uwer Rollup of 12 pull requests Successful merges: - #159906 (Semantic check of `mut` restrictions) - #156527 (Move `std::io` tests to `alloctests` & add prelude) - #159525 (Stabilize passing 128-bit integers via vector registers with `asm!` on x86) - #160342 (Specialize `advance_by` method of `Fuse`) - #160358 (borrowck: Simplify deps to build compiler 30s faster) - #160375 (miri subtree update) - #106643 (Allow only implementing `Read::read_buf`) - #159499 (tests: prefer max-llvm-major-version over open LLVM ranges) - #159729 (allocations are allowed to grow (but not shrink)) - #159881 (fix: Do not stop `visible_parent_map` breadth-first search reaching children of `#[doc(hidden)]` modules) - #160189 (Move codegen_stmt_debuginfo to debuginfo.rs) - #160356 (Add more tests for `must_implement_one_of`)

Rollup merge of #159525 - folkertdev:stabilize-x86-i128-asm, r=Amanieu Stabilize passing 128-bit integers via vector registers with `asm!` on x86 tracking issue: #133416 reference PR: rust-lang/reference#2313 # Stabilization report ## Summary Stabilize passing 128-bit integers via vector registers with `asm!` on x86 and x86_64: ```rust // Use 128-bit integers with vector registers. let mut v = 0u128; asm!("/* {:x} */", in(xmm_reg) v); asm!("/* {:x} */", out(xmm_reg) v); asm!("/* {:y} */", in(ymm_reg) v); asm!("/* {:y} */", out(ymm_reg) v); asm!("/* {:z} */", in(zmm_reg) v); asm!("/* {:z} */", out(zmm_reg) v); ``` 32-bit and 64-bit integer types can already be passed via vector registers. LLVM has supported 128-bit integers since 2019, see llvm/llvm-project#42502, so `rustc` not supporting them seems like an oversight. This feature is part of [`asm_experimental_reg`](#133416). We're not stabilizing that feature as a whole, but only pull out part of it. ## History - #151059 ## Open questions None. r? Amanieu

folkertdev added 2 commits July 18, 2026 16:50

modify asm_experimental_reg example to not need x86_64

721e0a8

stabilize passing 128-bit integers via vector registers with asm! o…

b68b9bc

…n x86

folkertdev added A-inline-assembly Area: Inline assembly (`asm!(…)`) I-lang-nominated Nominated for discussion during a lang team meeting. labels Jul 18, 2026

rustbot assigned Amanieu Jul 18, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 18, 2026

taiki-e mentioned this pull request Jul 18, 2026

Tracking Issue for asm_experimental_reg #133416

Open

2 tasks

traviscross added P-lang-drag-1 Lang team prioritization drag level 1. https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang T-lang Relevant to the language team labels Jul 22, 2026

rust-rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Jul 22, 2026

traviscross added the I-lang-radar Items that are on lang's radar and will need eventual work or consideration. label Jul 22, 2026

rust-rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Jul 22, 2026

traviscross removed I-lang-nominated Nominated for discussion during a lang team meeting. P-lang-drag-1 Lang team prioritization drag level 1. https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang labels Jul 22, 2026

Amanieu approved these changes Jul 24, 2026

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ehuss mentioned this pull request Jul 28, 2026

Stabilize passing 128-bit integers via vector registers with asm! on x86 rust-lang/reference#2313

Open

traviscross added needs-reference-pr This language change needs an approved Reference PR to proceed. has-reference-pr This language change has an approved Reference PR. and removed needs-reference-pr This language change needs an approved Reference PR to proceed. labels Jul 28, 2026

rustbot mentioned this pull request Aug 1, 2026

Tracking issue for release notes of #159525: Stabilize passing 128-bit integers via vector registers with asm! on x86 #160344

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rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 1, 2026

JonathanBrouwer mentioned this pull request Aug 1, 2026

Rollup of 3 pull requests #160357

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jhpratt mentioned this pull request Aug 1, 2026

Rollup of 6 pull requests #160361

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jhpratt mentioned this pull request Aug 2, 2026

Rollup of 6 pull requests #160367

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This was referenced Aug 2, 2026

Rollup of 11 pull requests #160383

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Rollup of 12 pull requests #160388

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rust-bors Bot merged commit d0c52fb into rust-lang:main Aug 2, 2026
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rustbot added this to the 1.99.0 milestone Aug 2, 2026

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Stabilize passing 128-bit integers via vector registers with `asm!` on x86 - #159525

Stabilize passing 128-bit integers via vector registers with `asm!` on x86#159525
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Stabilization report

Summary

History

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