Improve checking for implicit derivatives sampling requirement

slang-capabilities.def:
- Add capability implicit_derivatives_sampling. This is currently added
  only for documentation purposes.

hlsl.meta.slang:
- Add "static_assert(__targetHasImplicitDerivatives()" always before
  __requireComputeDerivative(), except for fragmentprocessing
  functions where the capabilities imply implicit derivatives.
- Note that implicit_derivatives_sampling is not added as a
  requirement for two reasons:
  - GLSL has functions where the behavior changes depending on whether
    implicit derivatives are available or not (e.g.,
    texture()). However, the transitive requirements do not allow
    conditionally invoking _Texture.Sample() (would require
    implicit_derivatives_sampling) or _Texture.SampleLevelZero() (no
    requirement) without using complex __target_switch/__stage_switch
    constructs per call site. With regular if constructs, the GLSL
    texture() functions would inherit the requirement for
    implicit_derivatives_sampling, which is not desirable.
  - _Texture.CalculateLevelOfDetail() cannot be added with the
    implicit_derivatives_sampling requirement at this time, since it
    would result in unsatisfyable target requirements for capability
    GL_NV_compute_shader_derivatives in compute stage. This is
    possibly a bug in the capability set processing in Slang. To be
    determined later.

Update a handful of tests. Either:
- Add the missing capability that enables implicit derivatives in
  compute stage.
- Switch the test to use the fragment stage instead of the compute
  stage. Particularly, metal does not support compute derivatives.

Issue #8683

Author: skiminki-nv

docs/user-guide/a3-02-reference-capability-atoms.md

@@ -1124,6 +1124,20 @@ Compound Capabilities
 `image_size`
 > Capabilities required to query image (RWTexture) size info
 
+`implicit_derivatives_sampling`
+> Capabilities required for implicit derivatives sampling.
+> 
+> This capability is required by texture sampling functions such as `_Texture.Sample()`
+> where the level of detail is determined by implicit derivatives.
+> 
+> @remark In GLSL, implicit level-of-detail `texture()` functions use the base texture when
+> the implicit derivatives are unavailable. When this capability is not present, invocations of
+> these functions are translated to invocations of `_Texture.SampleLevelZero()`.
+> 
+> @remark Implicit derivatives for the compute stage can be enabled by declaring capability `GL_NV_compute_shader_derivatives` (GLSL),
+> `SPV_KHR_compute_shader_derivatives` (SPIR-V), or profile `cs_6_6` (HLSL).
+> 
+
 `memorybarrier`
 > Capabilities required to use sm_5_0 style memory barriers
 

source/slang/hlsl.meta.slang

@@ -700,7 +700,7 @@ struct _Texture<T:ITexelElement, Shape: __ITextureShape, let isArray:int, let is
 //@hidden:
 
 // Returns true when the stage supports implicit derivatives on the
-// target. This must match with compound capability `fragmentprocessing`.
+// target. This must match with capability `implicit_derivatives_sampling`.
 //
 [__readNone]
 [ForceInline]
@@ -982,6 +982,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(glsl_hlsl_metal_spirv, texture_querylod)]
     float CalculateLevelOfDetail(TextureCoord location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1008,6 +1009,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(glsl_hlsl_metal_spirv, texture_querylod)]
     float CalculateLevelOfDetailUnclamped(TextureCoord location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1068,6 +1070,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(cpp_cuda_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T Sample(vector<float, Shape.dimensions+isArray> location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1126,6 +1129,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(cpp_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T Sample(vector<float, Shape.dimensions+isArray> location, constexpr vector<int, Shape.planeDimensions> offset)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1157,6 +1161,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(cpp_glsl_hlsl_metal_spirv, texture_sm_4_1_clamp_fragment)]
     T Sample(vector<float, Shape.dimensions+isArray> location, constexpr vector<int, Shape.planeDimensions> offset, float clamp)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1184,6 +1189,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [ForceInline]
     T Sample(vector<float, Shape.dimensions+isArray> location, constexpr vector<int, Shape.planeDimensions> offset, float clamp, out uint status)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1217,6 +1223,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(cpp_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T SampleBias(vector<float, Shape.dimensions+isArray> location, float bias)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1247,6 +1254,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(cpp_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T SampleBias(vector<float, Shape.dimensions+isArray> location, float bias, constexpr vector<int, Shape.planeDimensions> offset)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1276,6 +1284,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(hlsl_spirv, sm_5_0)]
     T SampleBias(vector<float, Shape.dimensions+isArray> location, float bias, constexpr vector<int, Shape.planeDimensions> offset, float clamp, out uint status)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1305,6 +1314,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(glsl_hlsl_metal_spirv_wgsl, texture_shadowlod)]
     float SampleCmp(vector<float, Shape.dimensions+isArray> location, float compareValue)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1383,6 +1393,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(glsl_hlsl_metal_spirv_wgsl, texture_shadowlod)]
     float SampleCmp(vector<float, Shape.dimensions+isArray> location, float compareValue, constexpr vector<int, Shape.planeDimensions> offset)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1418,6 +1429,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,1,format>
     [require(hlsl_spirv, sm_5_0)]
     float SampleCmp(vector<float, Shape.dimensions+isArray> location, float compareValue, constexpr vector<int, Shape.planeDimensions> offset, float clamp, out uint status)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1889,6 +1901,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,access,isShadow,0,format>
     [require(glsl_hlsl_metal_spirv, texture_querylod)]
     float CalculateLevelOfDetail(SamplerState s, TextureCoord location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1912,6 +1925,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,access,isShadow,0,format>
     [require(glsl_hlsl_metal_spirv, texture_querylod)]
     float CalculateLevelOfDetailUnclamped(SamplerState s, TextureCoord location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1935,6 +1949,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,access,isShadow,0,format>
     [require(glsl_hlsl_metal_spirv, texture_querylod)]
     float CalculateLevelOfDetail(SamplerComparisonState s, TextureCoord location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -1958,6 +1973,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,access,isShadow,0,format>
     [require(glsl_hlsl_metal_spirv, texture_querylod)]
     float CalculateLevelOfDetailUnclamped(SamplerComparisonState s, TextureCoord location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2080,6 +2096,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(cpp_cuda_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T Sample(SamplerState s, vector<float, Shape.dimensions+isArray> location)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2183,6 +2200,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(cpp_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T Sample(SamplerState s, vector<float, Shape.dimensions+isArray> location, constexpr vector<int, Shape.planeDimensions> offset)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2246,6 +2264,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(cpp_glsl_hlsl_metal_spirv, texture_sm_4_0_fragment)]
     T Sample(SamplerState s, vector<float, Shape.dimensions+isArray> location, constexpr vector<int, Shape.planeDimensions> offset, float clamp)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2293,6 +2312,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [ForceInline]
     T Sample(SamplerState s, vector<float, Shape.dimensions+isArray> location, constexpr vector<int, Shape.planeDimensions> offset, float clamp, out uint status)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2327,6 +2347,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(cpp_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T SampleBias(SamplerState s, vector<float, Shape.dimensions+isArray> location, float bias)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2393,6 +2414,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(cpp_glsl_hlsl_metal_spirv_wgsl, texture_sm_4_0_fragment)]
     T SampleBias(SamplerState s, vector<float, Shape.dimensions+isArray> location, float bias, constexpr vector<int, Shape.planeDimensions> offset)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2454,6 +2476,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(hlsl_spirv, sm_5_0)]
     T SampleBias(SamplerState s, vector<float, Shape.dimensions+isArray> location, float bias, constexpr vector<int, Shape.planeDimensions> offset, float clamp, out uint status)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2485,6 +2508,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(glsl_hlsl_metal_spirv_wgsl, texture_shadowlod)]
     float SampleCmp(SamplerComparisonState s, vector<float, Shape.dimensions+isArray> location, float compareValue)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2571,6 +2595,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(glsl_hlsl_metal_spirv_wgsl, texture_shadowlod)]
     float SampleCmp(SamplerComparisonState s, vector<float, Shape.dimensions+isArray> location, float compareValue, constexpr vector<int, Shape.planeDimensions> offset)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {
@@ -2618,6 +2643,7 @@ extension _Texture<T,Shape,isArray,isMS,sampleCount,0,isShadow,0,format>
     [require(hlsl_spirv, sm_5_0)]
     float SampleCmp(SamplerComparisonState s, vector<float, Shape.dimensions+isArray> location, float compareValue, constexpr vector<int, Shape.planeDimensions> offset, float clamp, out uint status)
     {
+        static_assert(__targetHasImplicitDerivatives(), "This function requires capability 'implicit_derivatives_sampling'");
         __requireComputeDerivative();
         __target_switch
         {

source/slang/slang-capabilities.capdef

@@ -2033,6 +2033,23 @@ alias structuredbuffer = sm_4_0_version;
 /// [Compound]
 alias structuredbuffer_rw = sm_4_0_version;
 
+/// Capabilities required for implicit derivatives sampling.
+///
+/// This capability is required by texture sampling functions such as `_Texture.Sample()`
+/// where the level of detail is determined by implicit derivatives.
+///
+/// @remark In GLSL, implicit level-of-detail `texture()` functions use the base texture when
+/// the implicit derivatives are unavailable. When this capability is not present, invocations of
+/// these functions are translated to invocations of `_Texture.SampleLevelZero()`.
+///
+/// @remark Implicit derivatives for the compute stage can be enabled by declaring capability `GL_NV_compute_shader_derivatives` (GLSL),
+/// `SPV_KHR_compute_shader_derivatives` (SPIR-V), or profile `cs_6_6` (HLSL).
+///
+/// [compound]
+alias implicit_derivatives_sampling = fragment
+                                    | raytracingstages_compute_amplification_mesh + GL_NV_compute_shader_derivatives
+                                    ;
+
 /// Capabilities required to use fragment derivative operations (without GLSL derivativecontrol)
 /// [Compound]
 alias fragmentprocessing = fragment + _sm_5_0

tests/bindings/hlsl-to-cpp-combined.slang

@@ -12,6 +12,6 @@ RWStructuredBuffer<float4> outputBuffer;
 [numthreads(4, 1, 1)]
 void computeMain(int3 dispatchThreadID: SV_DispatchThreadID)
 {
-    //CHK:[[VAR:[A-Za-z_][A-Za-z_0-9]*]].[[TEX]].Sample([[VAR]].[[SMP]]
-    outputBuffer[0] = s2D.Sample(float2(0.5f, 0.5f));
+    //CHK:[[VAR:[A-Za-z_][A-Za-z_0-9]*]].[[TEX]].SampleLevel({{.*}}[[VAR]]{{.*}}[[SMP]]
+    outputBuffer[0] = s2D.SampleLevelZero(float2(0.5f, 0.5f));
 }

tests/bugs/gh-4305.slang

@@ -1,9 +1,9 @@
-//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl -DQUAD -DMODIFIER
-//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl -DMODIFIER
-//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl -DQUAD
-//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl
-//TEST(compute, vulkan):COMPARE_COMPUTE(filecheck-buffer=BUF):-vk -compute -entry computeMain -output-using-type -emit-spirv-via-glsl -allow-glsl -xslang -DQUAD
-//TEST(compute, vulkan):COMPARE_COMPUTE(filecheck-buffer=BUF):-vk -compute -entry computeMain -output-using-type -emit-spirv-via-glsl -allow-glsl
+//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl -capability GL_NV_compute_shader_derivatives -DQUAD -DMODIFIER
+//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl -capability GL_NV_compute_shader_derivatives -DMODIFIER
+//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl -capability GL_NV_compute_shader_derivatives -DQUAD
+//TEST:SIMPLE(filecheck=CHECK): -stage compute  -entry computeMain -target glsl -allow-glsl -capability GL_NV_compute_shader_derivatives
+//TEST(compute, vulkan):COMPARE_COMPUTE(filecheck-buffer=BUF):-vk -compute -entry computeMain -output-using-type -emit-spirv-via-glsl -allow-glsl -capability GL_NV_compute_shader_derivatives -xslang -DQUAD
+//TEST(compute, vulkan):COMPARE_COMPUTE(filecheck-buffer=BUF):-vk -compute -entry computeMain -output-using-type -emit-spirv-via-glsl -allow-glsl -capability GL_NV_compute_shader_derivatives
 
 //TEST_INPUT: ubuffer(data=[0], stride=4):out,name outputBuffer
 RWStructuredBuffer<float> outputBuffer;

tests/compute/derivative-group-quad-validation.slang

@@ -1,4 +1,4 @@
-//TEST:SIMPLE(filecheck=CHECK): -target spirv-asm
+//TEST:SIMPLE(filecheck=CHECK): -target spirv-asm -capability SPV_KHR_compute_shader_derivatives
 //TEST_INPUT:ubuffer(data=[0], stride=4):out
 
 // Test that DerivativeGroupQuadsKHR execution mode validates workgroup size
@@ -23,4 +23,4 @@ void main() {
     g_ssbo[0] = texture_color;
 }
 
-// CHECK: error 31210: compute derivative group quad requires thread dispatch count of X and Y to each be at a multiple of 2
+// CHECK: error 31210: compute derivative group quad requires thread dispatch count of X and Y to each be at a multiple of 2

tests/cross-compile/cpp-resource.slang

@@ -39,15 +39,15 @@ void computeMain(
     float2 loc = dispatchThreadID.xy * 0.5f;
 
     float v = tex.Load(int3(tid, tid, 0));
-    float s = tex.Sample(sampler, loc);
+    float s = tex.SampleLevel(sampler, loc, 0.0f);
 
     // This should promote the 0.0 into a float2, 
-    float l = tex.Sample(sampler, 0.0);
+    float l = tex.SampleLevel(sampler, 0.0, 0.0f);
 
     float3 m = float(3).xxx;
 
     float3 arr[2] = { float3(3), float3(4) };
     doSomething(int(tid), arr);
 
     outputBuffer[tid] = int(tid * tid) + thing.a + thing3.a + int(v + s) + value + fromScalar.y + int(another.y) + int(m.x) + int(l) + int(arr[0].y); // + thing.a;
-}
+}

tests/cuda/cuda-texture.slang

@@ -18,5 +18,5 @@ void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
     float v = 1.0f - u;
     float2 uv = float2(u, v);
 
-    outputBuffer[tid] = texture.Sample(sampler, uv);
+    outputBuffer[tid] = texture.SampleLevel(sampler, uv, 0.0f);
 }