add trait `ScalarOrVectorComposite` #441

Firestar99 · 2025-10-14T17:27:01Z

Requires #440

rust-gpu/crates/spirv-std/src/scalar_or_vector.rs

Lines 23 to 57 in 6a62178

    
           /// A `VectorOrScalarComposite` is a type that is either 
        
           /// * a [`Scalar`] 
        
           /// * a [`Vector`] 
        
           /// * an array of `VectorOrScalarComposite` 
        
           /// * a struct where all members are `VectorOrScalarComposite` 
        
           /// * an enum with a `repr` that is a [`Scalar`] 
        
           /// 
        
           /// By calling [`Self::transform`] you can visit all the individual [`Scalar`] and [`Vector`] values this composite is 
        
           /// build out of and transform them into some other value. This is particularly useful for subgroup intrinsics sending 
        
           /// data to other threads. 
        
           /// 
        
           /// To derive `#[derive(VectorOrScalarComposite)]` on a struct, all members must also implement 
        
           /// `VectorOrScalarComposite`. 
        
           /// 
        
           /// To derive it on an enum, the enum must implement `From<N>` and `Into<N>` where `N` is defined by the `#[repr(N)]` 
        
           /// attribute on the enum and is an [`Integer`], like `u32`. 
        
           /// Note that some [safe subgroup operations] may return an "undefined result", so your `From<N>` must gracefully handle 
        
           /// arbitrary bit patterns being passed to it. While panicking is legal, it is discouraged as it may result in 
        
           /// unexpected control flow. 
        
           /// To implement these conversion traits, we recommend [`FromPrimitive`] and [`IntoPrimitive`] from the [`num_enum`] 
        
           /// crate. [`FromPrimitive`] requires that either the enum is exhaustive, or you provide it with a variant to default 
        
           /// to, by either implementing [`Default`] or marking a variant with `#[num_enum(default)]`. Note to disable default 
        
           /// features on the [`num_enum`] crate, or it won't compile on SPIR-V. 
        
           /// 
        
           /// [`Integer`]: crate::Integer 
        
           /// [subgroup operations]: crate::arch::subgroup_shuffle 
        
           /// [`FromPrimitive`]: https://docs.rs/num_enum/latest/num_enum/derive.FromPrimitive.html 
        
           /// [`IntoPrimitive`]: https://docs.rs/num_enum/latest/num_enum/derive.IntoPrimitive.html 
        
           /// [`num_enum`]: https://crates.io/crates/num_enum 
        
           pub trait ScalarOrVectorComposite: Copy + Send + Sync + 'static { 
        
               /// Transform the individual [`Scalar`] and [`Vector`] values of this type to a different value. 
        
               /// 
        
               /// See [`Self`] for more detail. 
        
               fn transform<F: ScalarOrVectorTransform>(self, f: &mut F) -> Self; 
        
           }

Also see previous iteration at #411

todo

derive enums
subgroup_all_equal()
subgroup_broadcast_const added in subgroup: fix docs and broadcast const variant #443

close #410

nazar-pc

Interesting, assuming this is zero cost abstraction (like when a struct contains a single scalar field I expect it to compile to the same code as if it was just a single scalar), this makes sense to me.

One opaque thing I do not like as much is that it can implicitly result in multiple subgroup operations. For example like when array is used it'll clearly iterate over each individual value instead of calling a vector form with all or part of the values, which may not be what the user would expect to happen.

Firestar99 · 2025-10-16T14:20:46Z

assuming this is zero cost abstraction

Pretty much, otherwise you'd see the subgroup compiletests with disassembly fail due to different codegen.

it can implicitly result in multiple subgroup operations

If you can't observe the difference between a single operation and multiple operations back-to-back, does that actually matter?
Also, you can expect all modern hardware to decompose any kind of vector op into multiple scalar ops, so us emitting actual vector ops won't give us any real benefit. Apart from maybe saving a few bytes of shader IR.

LegNeato · 2025-10-27T18:29:29Z

Going to let @eddyb review

Firestar99 · 2025-10-28T09:09:47Z

I'm surprised you say that, since this is only changing some ordinary rust code in spirv-std, defining that new trait and providing a derive for it. I didn't change any of the spirv intrinsics themselves.

Firestar99 mentioned this pull request Oct 14, 2025

Allow deriving VectorOrScalar #410

Open

Firestar99 force-pushed the scalar-or-vector-composite branch 2 times, most recently from ce822f1 to 5b6cf85 Compare October 14, 2025 17:37

nazar-pc reviewed Oct 15, 2025

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Firestar99 force-pushed the scalar-or-vector branch from 2143e1b to 80dda7d Compare October 16, 2025 09:26

Firestar99 force-pushed the scalar-or-vector-composite branch from 5b6cf85 to 5ebd674 Compare October 16, 2025 10:35

Firestar99 changed the title ~~ScalarOrVectorComposite~~ add trait ScalarOrVectorComposite Oct 16, 2025

Firestar99 force-pushed the scalar-or-vector-composite branch from 5ebd674 to 6a62178 Compare October 16, 2025 14:12

Firestar99 force-pushed the scalar-or-vector-composite branch from 6a62178 to 5a7d997 Compare October 16, 2025 14:23

Firestar99 mentioned this pull request Oct 16, 2025

derive spirv vector on user structs #411

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Firestar99 force-pushed the scalar-or-vector branch from 80dda7d to 449c894 Compare October 22, 2025 09:44

Firestar99 force-pushed the scalar-or-vector-composite branch from 5a7d997 to ceaceff Compare October 22, 2025 09:51

Firestar99 force-pushed the scalar-or-vector branch from 449c894 to e2d766b Compare October 22, 2025 10:25

Firestar99 force-pushed the scalar-or-vector-composite branch from ceaceff to 462a4fa Compare October 22, 2025 10:25

Firestar99 force-pushed the scalar-or-vector branch from e2d766b to 9a6d9ab Compare October 22, 2025 10:26

Firestar99 force-pushed the scalar-or-vector-composite branch from 462a4fa to bd37adb Compare October 22, 2025 10:29

Base automatically changed from scalar-or-vector to main October 22, 2025 12:59

Firestar99 force-pushed the scalar-or-vector-composite branch from bd37adb to 1a90208 Compare October 22, 2025 16:50

Firestar99 marked this pull request as ready for review October 22, 2025 16:50

Firestar99 requested review from LegNeato, eddyb and schell as code owners October 22, 2025 16:51

Firestar99 added 3 commits October 28, 2025 10:01

scalar or vector: add ScalarOrVectorComposite for subgroup intrinsics

df16a21

scalar or vector: add #[derive(ScalarOrVectorComposite)]

a240fb7

scalar or vector: adjust subgroup_all_equal to accept composites

06890d4

Firestar99 force-pushed the scalar-or-vector-composite branch from 1a90208 to 2a8211d Compare October 28, 2025 09:01

scalar or vector: derive enums and improve enum docs

0e4b51d

Firestar99 force-pushed the scalar-or-vector-composite branch from 2a8211d to 0e4b51d Compare October 28, 2025 09:06

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add trait `ScalarOrVectorComposite` #441

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Firestar99 commented Oct 14, 2025 •

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	/// A `VectorOrScalarComposite` is a type that is either
	/// * a [`Scalar`]
	/// * a [`Vector`]
	/// * an array of `VectorOrScalarComposite`
	/// * a struct where all members are `VectorOrScalarComposite`
	/// * an enum with a `repr` that is a [`Scalar`]
	///
	/// By calling [`Self::transform`] you can visit all the individual [`Scalar`] and [`Vector`] values this composite is
	/// build out of and transform them into some other value. This is particularly useful for subgroup intrinsics sending
	/// data to other threads.
	///
	/// To derive `#[derive(VectorOrScalarComposite)]` on a struct, all members must also implement
	/// `VectorOrScalarComposite`.
	///
	/// To derive it on an enum, the enum must implement `From<N>` and `Into<N>` where `N` is defined by the `#[repr(N)]`
	/// attribute on the enum and is an [`Integer`], like `u32`.
	/// Note that some [safe subgroup operations] may return an "undefined result", so your `From<N>` must gracefully handle
	/// arbitrary bit patterns being passed to it. While panicking is legal, it is discouraged as it may result in
	/// unexpected control flow.
	/// To implement these conversion traits, we recommend [`FromPrimitive`] and [`IntoPrimitive`] from the [`num_enum`]
	/// crate. [`FromPrimitive`] requires that either the enum is exhaustive, or you provide it with a variant to default
	/// to, by either implementing [`Default`] or marking a variant with `#[num_enum(default)]`. Note to disable default
	/// features on the [`num_enum`] crate, or it won't compile on SPIR-V.
	///
	/// [`Integer`]: crate::Integer
	/// [subgroup operations]: crate::arch::subgroup_shuffle
	/// [`FromPrimitive`]: https://docs.rs/num_enum/latest/num_enum/derive.FromPrimitive.html
	/// [`IntoPrimitive`]: https://docs.rs/num_enum/latest/num_enum/derive.IntoPrimitive.html
	/// [`num_enum`]: https://crates.io/crates/num_enum
	pub trait ScalarOrVectorComposite: Copy + Send + Sync + 'static {
	/// Transform the individual [`Scalar`] and [`Vector`] values of this type to a different value.
	///
	/// See [`Self`] for more detail.
	fn transform<F: ScalarOrVectorTransform>(self, f: &mut F) -> Self;
	}

add trait ScalarOrVectorComposite #441

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Firestar99 commented Oct 14, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Requires #440

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add trait `ScalarOrVectorComposite` #441

add trait `ScalarOrVectorComposite` #441

Firestar99 commented Oct 14, 2025 •

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