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

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

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

Pkgsrc changes: * Adapt to changes in vendored crate versions. * Version & checksum changes. Upstream changes: Version 1.99.0 (2026-10-01) ========================== Language -------- - [Add allow-by-default `raw_borrows_via_references` lint that checks for references that decay immediately into raw borrows](rust-lang/rust#138230) - [Extend `unconditional_panic` lint to function calls that panic when the chunks/windows size is zero] (rust-lang/rust#153563) - [Stabilize C-variadic function definitions] (rust-lang/rust#155697) - [Stabilize the ability to use `#[unsafe(naked)]` functions to define C-variadic functions (`#![feature(c_variadic_naked_functions)]`).] (rust-lang/rust#159746) - [Trait methods are now resolved on an adjusted never type (producing a FCW)] (rust-lang/rust#156047) - [Coerce from inference variables to trait objects if the inference variable is related via subtyping to a type that is known to be `Sized`] (rust-lang/rust#157820) - [Stabilize `#[my_macro] mod foo;`] (rust-lang/rust#157857). This allows outlined modules (`mod foo;`) anywhere in the body of a custom attribute or derive macro. - [Fix the `overflowing_literals` lint with repeated negation] (rust-lang/rust#158302). For instance, it will now no longer lint on `--128_i8`, which is already detected by the `arithmetic_overflow` lint. - [Add POSIX symbols to the `invalid_runtime_symbol_definitions` and `suspicious_runtime_symbol_definitions` lints] (rust-lang/rust#158522) - [Lint unused `#[path]` attributes on inline modules] (rust-lang/rust#158835) - [Enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group] (rust-lang/rust#159179) - [Stabilize passing 128-bit integers via vector registers with `asm!` on x86] (rust-lang/rust#159525) - [Explicitly document that some allocations are allowed to grow in-place (but none are allowed to shrink)] (rust-lang/rust#159729) - We now [guarantee] (rust-lang/rust#159730) that the contents of an `UnsafeCell` can be accessed without going through `get` - [The `invalid_reference_casting` lint was adjusted accordingly] (rust-lang/rust#159960) - [Account for globally enabled target features in `global_asm!`] (rust-lang/rust#160594) - [Warn if an invalid `doc` attribute is used on a macro invocation] (rust-lang/rust#161003) Compiler -------- - [Convert `-Ctarget-cpu` into a target-modifier for AVR, AMDGCN and NVPTX] (rust-lang/rust#150732) - [Enable `static_position_independent_executables` on all gnu and musl targets] (rust-lang/rust#158510) - When providing a suggestion about a missing method, rustc now prefers an exactly matching name from a [doc alias attribute] (https://doc.rust-lang.org/rustdoc/advanced-features.html#add-aliases-for-an-item-in-documentation-search) over a similarity search from other method names. If your new users sometimes expect a method under a different name, adding a doc alias will now help them find it via rustc suggestions, in addition to helping them find it via rustdoc search: [When suggesting method names, prefer *exact* doc aliases over similar names](rust-lang/rust#160369) Platform Support ---------------- - [Promote `riscv64-unknown-linux-musl` to Tier 2 with host tools] (rust-lang/rust#158766) Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. [platform-support-doc]: https://doc.rust-lang.org/rustc/platform-support.html Libraries --------- - Iteration on `RangeInclusive` (`a..=b` ranges) is now [optimized better in some circumstances] (rust-lang/rust#155114). As a side effect of this, the behavior of `RangeInclusive` values that has already been exhausted (as an iterator) has changed. For example, the return values of `start()` and `end()` on such ranges may return different values, and using such ranges as slice indexes may have different behavior. These behaviors were not guaranteed to be stable, so these changes are considered to not be breaking changes. - [Relax `transmute_copy` to accept `?Sized` types] (rust-lang/rust#155989) - [Update `transmute_copy` to use a non-unwinding panic] (rust-lang/rust#155989) - [Don't escape U+FF9E and U+FF9F in `escape_debug_ext`] (rust-lang/rust#158057) - [Re-export `core::fmt::NumBuffer` in `alloc` (and `std`)] (rust-lang/rust#161430) Stabilized APIs --------------- - [`IntoIterator` for `Box<[T; N]>`] (https://doc.rust-lang.org/stable/std/iter/trait.IntoIterator.html#impl-IntoIterator-for-Box%3C%5BT;+N%5D,+A%3E) - [`IntoIterator` for `&Box<[T; N]>`] (https://doc.rust-lang.org/stable/std/iter/trait.IntoIterator.html#impl-IntoIterator-for-%26Box%3C%5BT;+N%5D,+A%3E) - [`IntoIterator` for `&mut Box<[T; N]>`] (https://doc.rust-lang.org/stable/std/iter/trait.IntoIterator.html#impl-IntoIterator-for-%26mut+Box%3C%5BT;+N%5D,+A%3E) - [`VecDeque::retain_back`] (https://doc.rust-lang.org/stable/std/collections/struct.VecDeque.html#method.retain_back) - [`core::ffi::VaList`] (https://doc.rust-lang.org/stable/core/ffi/struct.VaList.html) - [`Box::into_non_null`] (https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#method.into_non_null) - [`Box::from_non_null`] (https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#method.from_non_null) - [`Vec::into_parts`] (https://doc.rust-lang.org/stable/std/vec/struct.Vec.html#method.into_parts) - [`Vec::from_parts`] (https://doc.rust-lang.org/stable/std/vec/struct.Vec.html#method.from_parts) - [`core::mem::size_of_val_raw`] (https://doc.rust-lang.org/stable/core/mem/fn.size_of_val_raw.html) - [`core::mem::align_of_val_raw`] (https://doc.rust-lang.org/stable/core/mem/fn.align_of_val_raw.html) - [`core::alloc::Layout::for_value_raw`] (https://doc.rust-lang.org/stable/core/alloc/struct.Layout.html#method.for_value_raw) - [`String::from_utf8_lossy_owned`] (https://doc.rust-lang.org/stable/std/string/struct.String.html#method.from_utf8_lossy_owned) - [`string::FromUtf8Error::into_utf8_lossy`] (https://doc.rust-lang.org/stable/std/string/struct.FromUtf8Error.html#method.into_utf8_lossy) - [`FusedIterator for StepBy<I>`] (https://doc.rust-lang.org/stable/std/iter/struct.StepBy.html#impl-FusedIterator-for-StepBy%3CI%3E) - [`std::fs::set_times`] (https://doc.rust-lang.org/stable/std/fs/fn.set_times.html) - [`std::fs::set_times_nofollow`] (https://doc.rust-lang.org/stable/std/fs/fn.set_times_nofollow.html) Cargo ----- - Add a new built-in profile `debug`. This is a preparation for transitioning the `dev` profile away from debugging to give a saner default for faster development iterations. Currently there is no difference between `dev` and `debug` profiles. [docs] (https://doc.rust-lang.org/nightly/cargo/reference/profiles.html#debug-1) [#17214] (rust-lang/cargo#17214) - Workspace members on edition 2024 or later can now override an inherited workspace dependency's `default-features` field. For example, `serde = { workspace = true, default-features = false }` now turns off default features even when the workspace definition enables them. On earlier editions, `default-features = false` is ignored with a warning. ([RFC 3945] (rust-lang/rfcs#3945)) [#17126](rust-lang/cargo#17126) - Incremental compilation is now disabled by default when running in CI. CI is detected via the CI environment variable. [#17220] (rust-lang/cargo#17220) See also the [full Cargo changelog] (https://doc.rust-lang.org/nightly/cargo/CHANGELOG.html#cargo-199-2026-10-01) Rustdoc ----- - [Add new `unused_footnote_definition` rustdoc lint] (rust-lang/rust#137858) - Smarter filtering of trait impls yields performance improvements of 20% on average and up to 40% on some real-world crates. ([1] (rust-lang/rust#159623), [2](rust-lang/rust#159721), [3](rust-lang/rust#159779), [4](rust-lang/rust#159854), [5](rust-lang/rust#159091)) Compatibility Notes ------------------- - [Fully deprecate the legacy integral modules] (rust-lang/rust#146882). For example, `std::i32::MAX` should be accessed via `i32::MAX` instead. - [Upgrade `no_mangle_generic_items` into hard error] (rust-lang/rust#154585) - [The `Pin::new_unchecked` has had its safety invariants changed slightly] (rust-lang/rust#156935) - [Do not promote references to extern statics] (rust-lang/rust#157641) - [Ensure that the inferred types of `let` patterns typecheck] (rust-lang/rust#157841) - [hermit/fs: Return `unsupported()` instead of `from_raw_os_error(22)`] (rust-lang/rust#158247) - [Fixed a bug where `#[repr(simd)]` was accidentally allowed on macro invocations on stable Rust] (rust-lang/rust#158523) - [Abort const-eval when there are generics in the type of the value being produced] (rust-lang/rust#159504) - [Attributes not applying to anything are now an error in code blocks in doc comments] (rust-lang/rust#159849) - [`Box::leak`: tell people to avoid unleaking] (rust-lang/rust#160323) - [PowerPC inline ASM: Fix scalar floats being in the wrong vector lane on little endian] (rust-lang/rust#160441) - [Do not take `doc(cfg())` into account when filtering doctests] (rust-lang/rust#159014) - [Infer anonymous lifetimes in the types of associated consts as `'static`] (rust-lang/rust#156508) - Macros that expand to a semicolon now produce a warning lint (`semicolon_in_expressions_from_non_local_macros`) even when the macro comes from another crate. Previously, such warnings only appeared for macros from the same crate, to avoid showing warnings that can't be fixed locally; however, this masked problems, as integration tests from the crate providing the macro get compiled as a separate crate, so tests often wouldn't reveal this issue. If you encounter a lint like this, please make sure to report it to the crate providing the macro so they can fix it; don't just silence it in your own crate. - [`semicolon_in_expressions_from_macros`: Lint on non-local macros too] (rust-lang/rust#159222) - [Split non-local `semicolon_in_expressions_from_macros` into a separate lint] (rust-lang/rust#159700) Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - [Update to LLVM 23] (rust-lang/rust#158734)

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

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Tracking Issue for asm_experimental_reg #133416

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

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

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Rollup of 3 pull requests #160357

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