move mod: make read_clock() better match glsl intrinsic

Author: Firestar99

crates/spirv-std/src/shader_clock.rs

@@ -3,53 +3,55 @@
 //! GLSL: [`GL_EXT_shader_realtime_clock`](https://github.com/KhronosGroup/GLSL/blob/main/extensions/ext/GL_EXT_shader_realtime_clock.txt)
 //! SPIRV: [`SPV_KHR_shader_clock`](https://github.khronos.org/SPIRV-Registry/extensions/KHR/SPV_KHR_shader_clock.html)
 
+#[cfg(target_arch = "spirv")]
+use crate::memory::Scope;
 #[cfg(target_arch = "spirv")]
 use core::arch::asm;
 use glam::UVec2;
 
-/// Read from the shader clock with either the `Subgroup` or `Device` scope.
+/// The [`read_clock`] function returns a 64-bit value representing a real-time clock that is globally coherent by
+/// all invocations on the GPU. See [`read_clock_uvec2`] for a variant that doesn't require 64-bit support.
+///
+/// clockRealtime2x32EXT() returns the same value encoded as a two-component vector of 32-bit unsigned integers with the first component containing the 32 least significant bits and the second component containing the 32 most significant bits.
 ///
-/// See: <https://github.khronos.org/SPIRV-Registry/extensions/KHR/SPV_KHR_shader_clock.html>
+/// The units of time are not defined for either of these operations and will wrap after exceeding the maximum value
+/// representable in 64 bits. These functions serve as code motion barriers.
 #[spirv_std_macros::gpu_only]
 #[doc(alias = "OpReadClockKHR")]
-pub fn read_clock_khr<const SCOPE: u32>() -> u64 {
+pub fn read_clock() -> u64 {
     unsafe {
-        let mut result: u64;
-
+        let mut result = Default::default();
         asm! {
             "%uint = OpTypeInt 32 0",
             "%scope = OpConstant %uint {scope}",
-            "{result} = OpReadClockKHR typeof*{result} %scope",
-            result = out(reg) result,
-            scope = const SCOPE,
+            "%result = OpReadClockKHR typeof*{result} %scope",
+            "OpStore {result} %result",
+            result = in(reg) &mut result,
+            scope = const (Scope::Device as u32),
         };
-
         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.'
+/// [`read_clock_uvec2`] returns the same value encoded as a two-component vector of 32-bit unsigned integers with the
+/// first component containing the 32 least significant bits and the second component containing the 32 most significant
+/// bits. See [`read_clock`] for a variant that returns a single `u64`.
 ///
-/// See:
-/// <https://htmlpreview.github.io/?https://github.com/KhronosGroup/SPIRV-Registry/blob/master/extensions/KHR/SPV_KHR_shader_clock.html>
+/// The units of time are not defined for either of these operations and will wrap after exceeding the maximum value
+/// representable in 64 bits. These functions serve as code motion barriers.
 #[spirv_std_macros::gpu_only]
 #[doc(alias = "OpReadClockKHR")]
-pub fn read_clock_uvec2_khr<const SCOPE: u32>() -> UVec2 {
+pub fn read_clock_uvec2() -> UVec2 {
     unsafe {
-        let mut result = UVec2::default();
-
+        let mut result = Default::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 SCOPE,
+            scope = const (Scope::Device as u32),
         };
-
         result
     }
 }

tests/compiletests/ui/arch/read_clock_khr.rs

@@ -5,12 +5,14 @@ use glam::UVec2;
 use spirv_std::spirv;
 use spirv_std::{
     memory::Scope,
-    shader_clock::{read_clock_khr, read_clock_uvec2_khr},
+    shader_clock::{read_clock, read_clock_uvec2},
 };
 
 #[spirv(fragment)]
-pub fn main() {
-    let clock_time = unsafe { read_clock_khr::<{ Scope::Subgroup as u32 }>() };
-
-    let clock_time_uvec2: UVec2 = unsafe { read_clock_uvec2_khr::<{ Scope::Subgroup as u32 }>() };
+pub fn main(out: &mut u32) {
+    unsafe {
+        let clock_time: u64 = read_clock();
+        let clock_time_uvec2: UVec2 = read_clock_uvec2();
+        *out = clock_time as u32 + clock_time_uvec2.x;
+    }
 }