Add an read_clock_khr function that calls OpReadClockKHR

crates/rustc_codegen_spirv/src/spirv_type_constraints.rs

@@ -745,7 +745,7 @@ pub fn instruction_signatures(op: Op) -> Option<&'static [InstSig<'static>]> {
         // SPV_AMD_shader_fragment_mask
         Op::FragmentMaskFetchAMD | Op::FragmentFetchAMD => reserved!(SPV_AMD_shader_fragment_mask),
         // SPV_KHR_shader_clock
-        Op::ReadClockKHR => reserved!(SPV_KHR_shader_clock),
+        Op::ReadClockKHR => {}
         // SPV_NV_mesh_shader
         Op::WritePackedPrimitiveIndices4x8NV => reserved!(SPV_NV_mesh_shader),
         // SPV_NV_ray_tracing

crates/spirv-std/src/arch.rs

@@ -150,3 +150,47 @@ pub unsafe fn vector_insert_dynamic<T: Scalar, V: Vector<T, N>, const N: usize>(
 pub fn kill() -> ! {
     unsafe { asm!("OpKill", options(noreturn)) }
 }
+
+/// Read from the subgroup shader clock.
+///
+/// Requires the `SPV_KHR_shader_clock` extension and both the `Int64` and `ShaderClockKHR` capabilities.
+///
+/// See:
+/// <https://htmlpreview.github.io/?https://github.com/KhronosGroup/SPIRV-Registry/blob/master/extensions/KHR/SPV_KHR_shader_clock.html>
+#[cfg(target_feature = "Int64")]
+#[spirv_std_macros::gpu_only]
+#[doc(alias = "OpReadClockKHR")]
+pub unsafe fn read_clock_khr() -> u64 {
+    let mut result: u64;
+
+    asm! {
+        "%uint = OpTypeInt 32 0",
+        "%scope = OpConstant %uint {scope}",
+        "{result} = OpReadClockKHR typeof*{result} %scope",
+        result = out(reg) result,
+        scope = const crate::memory::Scope::Subgroup as _,
+    };
+
+    result
+}
+
+/// Like `read_clock_khr` but returns a vector to avoid requiring the `Int64`
+/// capability. It returns a 'vector of two-components of 32-bit unsigned
+/// integer type with the first component containing the 32 least significant
+/// bits and the second component containing the 32 most significant bits.'
+#[spirv_std_macros::gpu_only]
+#[doc(alias = "OpReadClockKHR")]
+pub unsafe fn read_clock_uvec2_khr<V: Vector<u32, 2>>() -> V {
+    let mut result = V::default();
+
+    asm! {
+        "%uint = OpTypeInt 32 0",
+        "%scope = OpConstant %uint {scope}",
+        "%result = OpReadClockKHR typeof*{result} %scope",
+        "OpStore {result} %result",
+        result = in(reg) &mut result,
+        scope = const crate::memory::Scope::Subgroup as _,
+    };
+
+    result
+}

tests/ui/arch/read_clock_khr.rs

@@ -0,0 +1,16 @@
+// build-pass
+// compile-flags: -Ctarget-feature=+Int64,+ShaderClockKHR,+ext:SPV_KHR_shader_clock
+
+use glam::UVec2;
+use spirv_std::arch::{read_clock_khr, read_clock_uvec2_khr};
+
+#[spirv(fragment)]
+pub fn main() {
+    let clock_time = unsafe {
+        read_clock_khr()
+    };
+
+    let clock_time_uvec2: UVec2 = unsafe {
+        read_clock_uvec2_khr()
+    };
+}