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Spec changes for atomic vec2u #5610

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Mar 22, 2026
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Peter McNeeley committed Mar 24, 2026
commit a893387649afbc2d56b1b81086ce6290d2d71495
18 changes: 8 additions & 10 deletions wgsl/index.bs
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Expand Up @@ -1863,8 +1863,8 @@ The valid [=enable-extensions=] are listed in the following table.
<tr><td><dfn noexport dfn-for="extension">`atomic_vec2u_min_max`</dfn>
<td>[=atomic-vec2u-min-max|"atomic-vec2u-min-max"=]
<td>The built-in functions [[#atomic-store-min|atomicStoreMin]] and
[[#atomic-store-max|atomicStoreMax]] are valid to use on `atomic<vec2u>`
objects in the WGSL module. Otherwise, using these will result in a
[[#atomic-store-max|atomicStoreMax]] are valid to use on atomic&lt;[=vec2u=]&gt;
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@alan-baker alan-baker Apr 6, 2026

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Nit: I'd definitely link atomic to atomic types here.

types in the [=address spaces/storage=] address space. Otherwise, using these will result in a
[=shader-creation error=].
</table>

Expand Down Expand Up @@ -2009,11 +2009,6 @@ Extension names are not [=identifiers=]: they do not [=resolves|resolve=] to [=d
<td>
Supports the [=built-in values/global_invocation_index=] and
[=built-in values/workgroup_index=] [=built-in values=].
<tr><td><dfn for="language_extension">atomic_vec2u_min_max</dfn>
<td>
Supports the [[#atomic-store-min|atomicStoreMin]] and
[[#atomic-store-max|atomicStoreMax]] built-in functions
on [[#atomic-types|atomic&lt;vec2u&gt;]] objects.

</table>

Expand Down Expand Up @@ -3061,7 +3056,7 @@ An <dfn noexport>atomic type</dfn> encapsulates a [=type/concrete=] [=integer sc
<tr algorithm="atomic type"><td>atomic&lt;<dfn dfn-for="atomic" noexport>|T|</dfn>&gt;
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<td>Atomic of type |T|. Unless otherwise specified, |T| [=shader-creation error|must=] be either [=u32=] or [=i32=].
<tr algorithm="atomic type vecu"><td>atomic&lt;[=vec2u=]&gt;
<td>Atomic of type [=vec2u=]. A 64-bit atomic type via a composite. Requires the [=language_extension/atomic_vec2u_min_max=] extension.
<td>Atomic of type [=vec2u=]. This composite constitutes a 64-bit atomic type and is structurally equivalent to a bitcast. Requires the [=extension/atomic_vec2u_min_max=] extension.
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</table>

An expression [=shader-creation error|must not=] evaluate to an atomic type.
Expand Down Expand Up @@ -18986,7 +18981,7 @@ is, the `exchanged` member of the result structure may be `false` even if the
### Atomic Store Min and Max Functions ### {#atomic-store-min-max}

The functions in this section [=behavioral requirement|will=] be available only if
the [=language_extension/atomic_vec2u_min_max=] [=language extension=] is supported.
the [=extension/atomic_vec2u_min_max=] [=enable-extension=] is enabled.

Each function performs the following steps atomically:

Expand All @@ -18995,10 +18990,11 @@ Each function performs the following steps atomically:
name with the value |v|.
3. Store the new value using `atomic_ptr`.

The functions do not return any values.
The functions do not return a value.

For the functions in this section:
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@alan-baker alan-baker Apr 1, 2026

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Maybe hardcoding these constraints is better.

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@alan-baker alan-baker Apr 6, 2026

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With that done, these constraints can be removed.

- |T| [=shader-creation error|must=] be [=vec2u=].
- This composite operationally behaves as a single 64-bit unsigned integer scalar.
- `AS` [=shader-creation error|must=] be [=address spaces/storage=].

#### `atomicStoreMin` #### {#atomic-store-min}
Expand All @@ -19014,6 +19010,7 @@ with the value `v`.
<xmp highlight=wgsl>
// All operations are performed atomically
fn atomicStoreMin(atomic_ptr: ptr<AS, atomic<T>, read_write>, v : T) {
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// both 'old' and 'v' behave operationally as 64-bit unsigned integer scalars
let old = *atomic_ptr;
*atomic_ptr = min(old, v);
}
Expand All @@ -19033,6 +19030,7 @@ with the value `v`.
<xmp highlight=wgsl>
// All operations are performed atomically
fn atomicStoreMax(atomic_ptr: ptr<AS, atomic<T>, read_write>, v : T) {
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// both 'old' and 'v' behave operationally as 64-bit unsigned integer scalars
let old = *atomic_ptr;
*atomic_ptr = max(old, v);
}
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