Allow wgpu to use specialized dot4{I,U}8Packed

See #7574, in particular
<#7574 (comment)>.

Adds `FeaturesWGPU::NATIVE_PACKED_INTEGER_DOT_PRODUCT`, which is
available on `Adapter`s that support the specialized implementations for
`dot4I8Packed` and `dot4U8Packed` implemented in #7574 (currently, this
includes DX12 with Shader Model >= 6.4 and Vulkan with device extension
"VK_KHR_shader_integer_dot_product".

If this feature is requested during `Device` creation, the device is set
up such that `dot4I8Packed` and `dot4U8Packed` will be compiled to their
respective specialized instructions. This means that, on a vulkan
`Device`, the SPIR-V language version is set to 1.6, and the required
SPIR-V capabilities are marked as available (on DX12, requesting the
feature doesn't change anything since availability of the feature
already guarantees that Shader Model >= 6.4, which is all we need to
generate specialized code).

Author: robamler

wgpu-hal/src/dx12/adapter.rs

@@ -495,6 +495,12 @@ impl super::Adapter {
             atomic_int64_on_typed_resource_supported,
         );
 
+        // HLSL functions `dot4add_i8packed` and `dot4add_u8packed` are supported on SM >= 6.4.
+        features.set(
+            F::NATIVE_PACKED_INTEGER_DOT_PRODUCT,
+            shader_model >= naga::back::hlsl::ShaderModel::V6_4,
+        );
+
         // TODO: Determine if IPresentationManager is supported
         let presentation_timer = auxil::dxgi::time::PresentationTimer::new_dxgi();
 

wgpu-hal/src/vulkan/adapter.rs

@@ -841,6 +841,15 @@ impl PhysicalDeviceFeatures {
             F::EXPERIMENTAL_MESH_SHADER,
             caps.supports_extension(ext::mesh_shader::NAME),
         );
+
+        // The SPIR-V capabilities `DotProductInput4x8BitPackedKHR` and `DotProductKHR` seem to be
+        // implemented in the device extension `VK_KHR_shader_integer_dot_product`, see
+        // <https://registry.khronos.org/vulkan/specs/latest/man/html/VK_KHR_shader_integer_dot_product.html>.
+        features.set(
+            F::NATIVE_PACKED_INTEGER_DOT_PRODUCT,
+            caps.supports_extension(khr::shader_integer_dot_product::NAME),
+        );
+
         if let Some(ref mesh_shader) = self.mesh_shader {
             features.set(
                 F::EXPERIMENTAL_MESH_SHADER_MULTIVIEW,
@@ -2011,8 +2020,15 @@ impl super::Adapter {
             if features.contains(wgt::Features::EXPERIMENTAL_RAY_HIT_VERTEX_RETURN) {
                 capabilities.push(spv::Capability::RayQueryPositionFetchKHR)
             }
+            if features.contains(wgt::Features::NATIVE_PACKED_INTEGER_DOT_PRODUCT) {
+                capabilities.push(spv::Capability::DotProduct);
+                capabilities.push(spv::Capability::DotProductInput4x8BitPacked);
+            }
             spv::Options {
-                lang_version: if features
+                lang_version: if features.contains(wgt::Features::NATIVE_PACKED_INTEGER_DOT_PRODUCT)
+                {
+                    (1, 6)
+                } else if features
                     .intersects(wgt::Features::SUBGROUP | wgt::Features::SUBGROUP_VERTEX)
                 {
                     (1, 3)

wgpu-types/src/features.rs

@@ -1193,6 +1193,17 @@ bitflags_array! {
         ///
         /// This is a native only feature.
         const EXPERIMENTAL_MESH_SHADER_MULTIVIEW = 1 << 49;
+
+        /// Ensures that `dot4I8Packed` and `dot4U8Packed` in WGSL are compiled to specialized
+        /// intrinsics.
+        ///
+        /// Supported platforms:
+        /// - Vulkan (with SPIR-V 1.6+ and [DotProductInput4x8BitPackedKHR](https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#spirvenv-capabilities-table-DotProductInput4x8BitPacked))
+        /// - DX12 (with SM 6.4+)
+        ///
+        /// Potential Platforms:
+        /// - WebGPU
+        const NATIVE_PACKED_INTEGER_DOT_PRODUCT = 1 << 50;
     }
 
     /// Features that are not guaranteed to be supported.