[wgpu-hal] Add PrivateCapabilities::shader_int8 on Vulkan

This allows declaring the SPIR-V capability "Int8", which allows us to
generate faster code for `[un]pack4x{I, U}8[Clamp]`.

Author: robamler

wgpu-hal/src/vulkan/adapter.rs

@@ -40,6 +40,9 @@ pub struct PhysicalDeviceFeatures {
     /// Basic Vulkan 1.0 features.
     core: vk::PhysicalDeviceFeatures,
 
+    /// Vulkan 1.2 features.
+    vulkan12: Option<vk::PhysicalDeviceVulkan12Features<'static>>,
+
     /// Features provided by `VK_EXT_descriptor_indexing`, promoted to Vulkan 1.2.
     pub(super) descriptor_indexing:
         Option<vk::PhysicalDeviceDescriptorIndexingFeaturesEXT<'static>>,
@@ -136,6 +139,9 @@ impl PhysicalDeviceFeatures {
         mut info: vk::DeviceCreateInfo<'a>,
     ) -> vk::DeviceCreateInfo<'a> {
         info = info.enabled_features(&self.core);
+        if let Some(ref mut feature) = self.vulkan12 {
+            info = info.push_next(feature);
+        }
         if let Some(ref mut feature) = self.descriptor_indexing {
             info = info.push_next(feature);
         }
@@ -316,6 +322,14 @@ impl PhysicalDeviceFeatures {
                 .geometry_shader(requested_features.contains(wgt::Features::SHADER_PRIMITIVE_INDEX))
                 .depth_clamp(requested_features.contains(wgt::Features::DEPTH_CLIP_CONTROL))
                 .dual_src_blend(requested_features.contains(wgt::Features::DUAL_SOURCE_BLENDING)),
+            vulkan12: if device_api_version >= vk::API_VERSION_1_2 {
+                Some(
+                    vk::PhysicalDeviceVulkan12Features::default()
+                        .shader_int8(private_caps.shader_int8),
+                )
+            } else {
+                None
+            },
             descriptor_indexing: if requested_features.intersects(INDEXING_FEATURES) {
                 Some(
                     vk::PhysicalDeviceDescriptorIndexingFeaturesEXT::default()
@@ -1390,6 +1404,13 @@ impl super::InstanceShared {
             let core = vk::PhysicalDeviceFeatures::default();
             let mut features2 = vk::PhysicalDeviceFeatures2KHR::default().features(core);
 
+            if capabilities.device_api_version >= vk::API_VERSION_1_2 {
+                let next = features
+                    .vulkan12
+                    .insert(vk::PhysicalDeviceVulkan12Features::default());
+                features2 = features2.push_next(next);
+            }
+
             // `VK_KHR_multiview` is promoted to 1.1
             if capabilities.device_api_version >= vk::API_VERSION_1_1
                 || capabilities.supports_extension(khr::multiview::NAME)
@@ -1714,6 +1735,9 @@ impl super::Instance {
             shader_integer_dot_product: phd_features
                 .shader_integer_dot_product
                 .is_some_and(|ext| ext.shader_integer_dot_product != 0),
+            shader_int8: phd_features
+                .vulkan12
+                .is_some_and(|features| features.shader_int8 != 0),
         };
         let capabilities = crate::Capabilities {
             limits: phd_capabilities.to_wgpu_limits(),
@@ -2015,6 +2039,10 @@ impl super::Adapter {
                     spv::Capability::DotProductKHR,
                 ]);
             }
+            if self.private_caps.shader_int8 {
+                // See <https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkPhysicalDeviceVulkan12Features.html#features-shaderInt8>.
+                capabilities.extend(&[spv::Capability::Int8]);
+            }
             spv::Options {
                 lang_version: match self.phd_capabilities.device_api_version {
                     // Use maximum supported SPIR-V version according to

wgpu-hal/src/vulkan/mod.rs

@@ -536,6 +536,19 @@ struct PrivateCapabilities {
     ///
     /// [`VK_KHR_shader_integer_dot_product`]: https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_KHR_shader_integer_dot_product.html
     shader_integer_dot_product: bool,
+
+    /// True if this adapter supports 8-bit integers (possible in Vulkan 1.2+).
+    ///
+    /// Allows shaders to declare the "Int8" capability. Note, however, that this
+    /// feature alone allows the use of 8-bit integers "only in the `Private`,
+    /// `Workgroup` (for non-Block variables), and `Function` storage classes"
+    /// ([see spec]). To use 8-bit integers in the interface storage classes (e.g.,
+    /// `StorageBuffer`), you also need to enable the corresponding feature in
+    /// `VkPhysicalDevice8BitStorageFeatures` and declare the corresponding SPIR-V
+    /// capability (e.g., `StorageBuffer8BitAccess`).
+    ///
+    /// [see spec]: https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkPhysicalDeviceVulkan12Features.html#features-shaderInt8
+    shader_int8: bool,
 }
 
 bitflags::bitflags!(