[spirv] Add support for SV_Barycentrics (#837)

The translation is done using  SPIR-V Extension
SPV_AMD_shader_explicit_vertex_parameter.

docs/SPIR-V.rst

@@ -854,6 +854,8 @@ some system-value (SV) semantic strings will be translated into SPIR-V
 +---------------------------+-------------+--------------------------+-----------------------+-----------------------+
 | SV_StencilRef             | PSOut       | ``FragStencilRefEXT``    | N/A                   | ``StencilExportEXT``  |
 +---------------------------+-------------+--------------------------+-----------------------+-----------------------+
+| SV_Barycentrics           | PSIn        | ``BaryCoord*AMD``        | N/A                   | ``Shader``            |
++---------------------------+-------------+--------------------------+-----------------------+-----------------------+
 |                           | GSOut       | ``Layer``                | N/A                   | ``Geometry``          |
 | SV_RenderTargetArrayIndex +-------------+--------------------------+-----------------------+-----------------------+
 |                           | PSIn        | ``Layer``                | N/A                   | ``Geometry``          |

tools/clang/lib/SPIRV/DeclResultIdMapper.cpp

@@ -944,6 +944,9 @@ bool DeclResultIdMapper::createStageVars(
     case hlsl::Semantic::Kind::Coverage:
       typeId = theBuilder.getArrayType(typeId, theBuilder.getConstantUint32(1));
       break;
+    case hlsl::Semantic::Kind::Barycentrics:
+      typeId = theBuilder.getVecType(theBuilder.getFloat32Type(), 2);
+      break;
     }
 
     // Handle the extra arrayness
@@ -959,7 +962,7 @@ bool DeclResultIdMapper::createStageVars(
     const std::string semanticStr = stageVar.getSemanticStr();
     llvm::Twine name = namePrefix + "." + semanticStr;
     const uint32_t varId =
-        createSpirvStageVar(&stageVar, name, semanticToUse->loc);
+        createSpirvStageVar(&stageVar, decl, name, semanticToUse->loc);
 
     if (varId == 0)
       return false;
@@ -978,7 +981,9 @@ bool DeclResultIdMapper::createStageVars(
       theBuilder.decorate(varId, spv::Decoration::Patch);
 
     // Decorate with interpolation modes for pixel shader input variables
-    if (shaderModel.IsPS() && sigPoint->IsInput())
+    if (shaderModel.IsPS() && sigPoint->IsInput() &&
+        // BaryCoord*AMD buitins already encode the interpolation mode.
+        semanticKind != hlsl::Semantic::Kind::Barycentrics)
       decoratePSInterpolationMode(decl, type, varId);
 
     if (asInput) {
@@ -1028,6 +1033,21 @@ bool DeclResultIdMapper::createStageVars(
       else if (semanticKind == hlsl::Semantic::Kind::Coverage) {
         *value = theBuilder.createCompositeExtract(srcTypeId, *value, {0});
       }
+      // Special handling of SV_Barycentrics, which is a float3, but the
+      // underlying stage input variable is a float2 (only provides the first
+      // two components). Calculate the third element.
+      else if (semanticKind == hlsl::Semantic::Kind::Barycentrics) {
+        const auto f32Type = theBuilder.getFloat32Type();
+        const auto x = theBuilder.createCompositeExtract(f32Type, *value, {0});
+        const auto y = theBuilder.createCompositeExtract(f32Type, *value, {1});
+        const auto xy =
+            theBuilder.createBinaryOp(spv::Op::OpFAdd, f32Type, x, y);
+        const auto z = theBuilder.createBinaryOp(
+            spv::Op::OpFSub, f32Type, theBuilder.getConstantFloat32(1), xy);
+        const auto v3f32Type = theBuilder.getVecType(f32Type, 3);
+
+        *value = theBuilder.createCompositeConstruct(v3f32Type, {x, y, z});
+      }
     } else {
       if (noWriteBack)
         return true;
@@ -1275,6 +1295,7 @@ void DeclResultIdMapper::decoratePSInterpolationMode(const DeclaratorDecl *decl,
 }
 
 uint32_t DeclResultIdMapper::createSpirvStageVar(StageVar *stageVar,
+                                                 const DeclaratorDecl *decl,
                                                  const llvm::Twine &name,
                                                  SourceLocation srcLoc) {
   using spv::BuiltIn;
@@ -1505,6 +1526,33 @@ uint32_t DeclResultIdMapper::createSpirvStageVar(StageVar *stageVar,
     stageVar->setIsSpirvBuiltin();
     return theBuilder.addStageBuiltinVar(type, sc, BuiltIn::FragStencilRefEXT);
   }
+  // According to DXIL spec, the ViewID SV can only be used by PSIn.
+  case hlsl::Semantic::Kind::Barycentrics: {
+    theBuilder.addExtension("SPV_AMD_shader_explicit_vertex_parameter");
+    stageVar->setIsSpirvBuiltin();
+
+    // Selecting the correct builtin according to interpolation mode
+    auto bi = BuiltIn::Max;
+    if (decl->hasAttr<HLSLNoPerspectiveAttr>()) {
+      if (decl->hasAttr<HLSLCentroidAttr>()) {
+        bi = BuiltIn::BaryCoordNoPerspCentroidAMD;
+      } else if (decl->hasAttr<HLSLSampleAttr>()) {
+        bi = BuiltIn::BaryCoordNoPerspSampleAMD;
+      } else {
+        bi = BuiltIn::BaryCoordNoPerspAMD;
+      }
+    } else {
+      if (decl->hasAttr<HLSLCentroidAttr>()) {
+        bi = BuiltIn::BaryCoordSmoothCentroidAMD;
+      } else if (decl->hasAttr<HLSLSampleAttr>()) {
+        bi = BuiltIn::BaryCoordSmoothSampleAMD;
+      } else {
+        bi = BuiltIn::BaryCoordSmoothAMD;
+      }
+    }
+
+    return theBuilder.addStageBuiltinVar(type, sc, bi);
+  }
   // According to DXIL spec, the RenderTargetArrayIndex SV can only be used by
   // VSIn, VSOut, HSCPIn, HSCPOut, DSIn, DSOut, GSVIn, GSOut, PSIn.
   // According to Vulkan spec, the Layer BuiltIn can only be used in GSOut and

tools/clang/lib/SPIRV/DeclResultIdMapper.h

@@ -397,8 +397,8 @@ private:
   /// the <result-id>. Also sets whether the StageVar is a SPIR-V builtin and
   /// its storage class accordingly. name will be used as the debug name when
   /// creating a stage input/output variable.
-  uint32_t createSpirvStageVar(StageVar *, const llvm::Twine &name,
-                               SourceLocation);
+  uint32_t createSpirvStageVar(StageVar *, const DeclaratorDecl *decl,
+                               const llvm::Twine &name, SourceLocation);
 
   /// Creates the associated counter variable for RW/Append/Consume
   /// structured buffer.

tools/clang/test/CodeGenSPIRV/semantic.barycentrics.ps.np-c.hlsl

@@ -0,0 +1,22 @@
+// Run: %dxc -T ps_6_1 -E main
+
+// CHECK:      OpExtension "SPV_AMD_shader_explicit_vertex_parameter"
+
+// CHECK:      OpEntryPoint Fragment
+// CHECK-SAME: [[bary:%\d+]]
+
+// CHECK:      OpDecorate [[bary]] BuiltIn BaryCoordNoPerspCentroidAMD
+
+// CHECK:      [[bary]] = OpVariable %_ptr_Input_v2float Input
+
+float4 main(noperspective centroid float3 bary : SV_Barycentrics) : SV_Target {
+    return float4(bary, 1.0);
+// CHECK:      %param_var_bary = OpVariable %_ptr_Function_v3float Function
+// CHECK-NEXT:     [[c2:%\d+]] = OpLoad %v2float [[bary]]
+// CHECK-NEXT:      [[x:%\d+]] = OpCompositeExtract %float [[c2]] 0
+// CHECK-NEXT:      [[y:%\d+]] = OpCompositeExtract %float [[c2]] 1
+// CHECK-NEXT:     [[xy:%\d+]] = OpFAdd %float [[x]] [[y]]
+// CHECK-NEXT:      [[z:%\d+]] = OpFSub %float %float_1 [[xy]]
+// CHECK-NEXT:     [[c3:%\d+]] = OpCompositeConstruct %v3float [[x]] [[y]] [[z]]
+// CHECK-NEXT:                   OpStore %param_var_bary [[c3]]
+}

tools/clang/test/CodeGenSPIRV/semantic.barycentrics.ps.np-s.hlsl

@@ -0,0 +1,22 @@
+// Run: %dxc -T ps_6_1 -E main
+
+// CHECK:      OpExtension "SPV_AMD_shader_explicit_vertex_parameter"
+
+// CHECK:      OpEntryPoint Fragment
+// CHECK-SAME: [[bary:%\d+]]
+
+// CHECK:      OpDecorate [[bary]] BuiltIn BaryCoordNoPerspSampleAMD
+
+// CHECK:      [[bary]] = OpVariable %_ptr_Input_v2float Input
+
+float4 main(noperspective sample float3 bary : SV_Barycentrics) : SV_Target {
+    return float4(bary, 1.0);
+// CHECK:      %param_var_bary = OpVariable %_ptr_Function_v3float Function
+// CHECK-NEXT:     [[c2:%\d+]] = OpLoad %v2float [[bary]]
+// CHECK-NEXT:      [[x:%\d+]] = OpCompositeExtract %float [[c2]] 0
+// CHECK-NEXT:      [[y:%\d+]] = OpCompositeExtract %float [[c2]] 1
+// CHECK-NEXT:     [[xy:%\d+]] = OpFAdd %float [[x]] [[y]]
+// CHECK-NEXT:      [[z:%\d+]] = OpFSub %float %float_1 [[xy]]
+// CHECK-NEXT:     [[c3:%\d+]] = OpCompositeConstruct %v3float [[x]] [[y]] [[z]]
+// CHECK-NEXT:                   OpStore %param_var_bary [[c3]]
+}

tools/clang/test/CodeGenSPIRV/semantic.barycentrics.ps.np.hlsl

@@ -0,0 +1,22 @@
+// Run: %dxc -T ps_6_1 -E main
+
+// CHECK:      OpExtension "SPV_AMD_shader_explicit_vertex_parameter"
+
+// CHECK:      OpEntryPoint Fragment
+// CHECK-SAME: [[bary:%\d+]]
+
+// CHECK:      OpDecorate [[bary]] BuiltIn BaryCoordNoPerspAMD
+
+// CHECK:      [[bary]] = OpVariable %_ptr_Input_v2float Input
+
+float4 main(noperspective float3 bary : SV_Barycentrics) : SV_Target {
+    return float4(bary, 1.0);
+// CHECK:      %param_var_bary = OpVariable %_ptr_Function_v3float Function
+// CHECK-NEXT:     [[c2:%\d+]] = OpLoad %v2float [[bary]]
+// CHECK-NEXT:      [[x:%\d+]] = OpCompositeExtract %float [[c2]] 0
+// CHECK-NEXT:      [[y:%\d+]] = OpCompositeExtract %float [[c2]] 1
+// CHECK-NEXT:     [[xy:%\d+]] = OpFAdd %float [[x]] [[y]]
+// CHECK-NEXT:      [[z:%\d+]] = OpFSub %float %float_1 [[xy]]
+// CHECK-NEXT:     [[c3:%\d+]] = OpCompositeConstruct %v3float [[x]] [[y]] [[z]]
+// CHECK-NEXT:                   OpStore %param_var_bary [[c3]]
+}

tools/clang/test/CodeGenSPIRV/semantic.barycentrics.ps.s-c.hlsl

@@ -0,0 +1,22 @@
+// Run: %dxc -T ps_6_1 -E main
+
+// CHECK:      OpExtension "SPV_AMD_shader_explicit_vertex_parameter"
+
+// CHECK:      OpEntryPoint Fragment
+// CHECK-SAME: [[bary:%\d+]]
+
+// CHECK:      OpDecorate [[bary]] BuiltIn BaryCoordSmoothCentroidAMD
+
+// CHECK:      [[bary]] = OpVariable %_ptr_Input_v2float Input
+
+float4 main(centroid float3 bary : SV_Barycentrics) : SV_Target {
+    return float4(bary, 1.0);
+// CHECK:      %param_var_bary = OpVariable %_ptr_Function_v3float Function
+// CHECK-NEXT:     [[c2:%\d+]] = OpLoad %v2float [[bary]]
+// CHECK-NEXT:      [[x:%\d+]] = OpCompositeExtract %float [[c2]] 0
+// CHECK-NEXT:      [[y:%\d+]] = OpCompositeExtract %float [[c2]] 1
+// CHECK-NEXT:     [[xy:%\d+]] = OpFAdd %float [[x]] [[y]]
+// CHECK-NEXT:      [[z:%\d+]] = OpFSub %float %float_1 [[xy]]
+// CHECK-NEXT:     [[c3:%\d+]] = OpCompositeConstruct %v3float [[x]] [[y]] [[z]]
+// CHECK-NEXT:                   OpStore %param_var_bary [[c3]]
+}

tools/clang/test/CodeGenSPIRV/semantic.barycentrics.ps.s-s.hlsl

@@ -0,0 +1,22 @@
+// Run: %dxc -T ps_6_1 -E main
+
+// CHECK:      OpExtension "SPV_AMD_shader_explicit_vertex_parameter"
+
+// CHECK:      OpEntryPoint Fragment
+// CHECK-SAME: [[bary:%\d+]]
+
+// CHECK:      OpDecorate [[bary]] BuiltIn BaryCoordSmoothSampleAMD
+
+// CHECK:      [[bary]] = OpVariable %_ptr_Input_v2float Input
+
+float4 main(sample float3 bary : SV_Barycentrics) : SV_Target {
+    return float4(bary, 1.0);
+// CHECK:      %param_var_bary = OpVariable %_ptr_Function_v3float Function
+// CHECK-NEXT:     [[c2:%\d+]] = OpLoad %v2float [[bary]]
+// CHECK-NEXT:      [[x:%\d+]] = OpCompositeExtract %float [[c2]] 0
+// CHECK-NEXT:      [[y:%\d+]] = OpCompositeExtract %float [[c2]] 1
+// CHECK-NEXT:     [[xy:%\d+]] = OpFAdd %float [[x]] [[y]]
+// CHECK-NEXT:      [[z:%\d+]] = OpFSub %float %float_1 [[xy]]
+// CHECK-NEXT:     [[c3:%\d+]] = OpCompositeConstruct %v3float [[x]] [[y]] [[z]]
+// CHECK-NEXT:                   OpStore %param_var_bary [[c3]]
+}

tools/clang/test/CodeGenSPIRV/semantic.barycentrics.ps.s.hlsl

@@ -0,0 +1,22 @@
+// Run: %dxc -T ps_6_1 -E main
+
+// CHECK:      OpExtension "SPV_AMD_shader_explicit_vertex_parameter"
+
+// CHECK:      OpEntryPoint Fragment
+// CHECK-SAME: [[bary:%\d+]]
+
+// CHECK:      OpDecorate [[bary]] BuiltIn BaryCoordSmoothAMD
+
+// CHECK:      [[bary]] = OpVariable %_ptr_Input_v2float Input
+
+float4 main(float3 bary : SV_Barycentrics) : SV_Target {
+    return float4(bary, 1.0);
+// CHECK:      %param_var_bary = OpVariable %_ptr_Function_v3float Function
+// CHECK-NEXT:     [[c2:%\d+]] = OpLoad %v2float [[bary]]
+// CHECK-NEXT:      [[x:%\d+]] = OpCompositeExtract %float [[c2]] 0
+// CHECK-NEXT:      [[y:%\d+]] = OpCompositeExtract %float [[c2]] 1
+// CHECK-NEXT:     [[xy:%\d+]] = OpFAdd %float [[x]] [[y]]
+// CHECK-NEXT:      [[z:%\d+]] = OpFSub %float %float_1 [[xy]]
+// CHECK-NEXT:     [[c3:%\d+]] = OpCompositeConstruct %v3float [[x]] [[y]] [[z]]
+// CHECK-NEXT:                   OpStore %param_var_bary [[c3]]
+}

tools/clang/unittests/SPIRV/CodeGenSPIRVTest.cpp

@@ -487,6 +487,25 @@ TEST_F(FileTest, SemanticViewportArrayIndexGS) {
 TEST_F(FileTest, SemanticViewportArrayIndexPS) {
   runFileTest("semantic.viewport-array-index.ps.hlsl");
 }
+TEST_F(FileTest, SemanticBarycentricsSmoothPS) {
+  runFileTest("semantic.barycentrics.ps.s.hlsl");
+}
+TEST_F(FileTest, SemanticBarycentricsSmoothCentroidPS) {
+  runFileTest("semantic.barycentrics.ps.s-c.hlsl");
+}
+TEST_F(FileTest, SemanticBarycentricsSmoothSamplePS) {
+  runFileTest("semantic.barycentrics.ps.s-s.hlsl");
+}
+TEST_F(FileTest, SemanticBarycentricsNoPerspectivePS) {
+  runFileTest("semantic.barycentrics.ps.np.hlsl");
+}
+TEST_F(FileTest, SemanticBarycentricsNoPerspectiveCentroidPS) {
+  runFileTest("semantic.barycentrics.ps.np-c.hlsl");
+}
+TEST_F(FileTest, SemanticBarycentricsNoPerspectiveSamplePS) {
+  runFileTest("semantic.barycentrics.ps.np-s.hlsl");
+}
+
 TEST_F(FileTest, SemanticCoveragePS) {
   runFileTest("semantic.coverage.ps.hlsl");
 }