[SPRIV] Allow vk-invert-y for MS shaders (#6839)

Fixes #3154

tools/clang/lib/SPIRV/DeclResultIdMapper.cpp

@@ -3667,7 +3667,7 @@ bool DeclResultIdMapper::createStageVars(StageVarDataBundle &stageVarData,
         return true;
       // Negate SV_Position.y if requested
       if (semanticKind == hlsl::Semantic::Kind::Position)
-        *value = invertYIfRequested(*value, thisSemantic.loc);
+        *value = theEmitter.invertYIfRequested(*value, thisSemantic.loc);
       storeToShaderOutputVariable(varInstr, *value, stageVarData);
     }
 
@@ -3856,7 +3856,7 @@ bool DeclResultIdMapper::writeBackOutputStream(const NamedDecl *decl,
 
     // Negate SV_Position.y if requested
     if (semanticInfo.semantic->GetKind() == hlsl::Semantic::Kind::Position)
-      value = invertYIfRequested(value, loc, range);
+      value = theEmitter.invertYIfRequested(value, loc, range);
 
     // Boolean stage output variables are represented as unsigned integers.
     if (isBooleanStageIOVar(decl, type, semanticInfo.semantic->GetKind(),
@@ -3906,22 +3906,6 @@ bool DeclResultIdMapper::writeBackOutputStream(const NamedDecl *decl,
   return true;
 }
 
-SpirvInstruction *
-DeclResultIdMapper::invertYIfRequested(SpirvInstruction *position,
-                                       SourceLocation loc, SourceRange range) {
-  // Negate SV_Position.y if requested
-  if (spirvOptions.invertY) {
-    const auto oldY = spvBuilder.createCompositeExtract(
-        astContext.FloatTy, position, {1}, loc, range);
-    const auto newY = spvBuilder.createUnaryOp(
-        spv::Op::OpFNegate, astContext.FloatTy, oldY, loc, range);
-    position = spvBuilder.createCompositeInsert(
-        astContext.getExtVectorType(astContext.FloatTy, 4), position, {1}, newY,
-        loc, range);
-  }
-  return position;
-}
-
 SpirvInstruction *
 DeclResultIdMapper::invertWIfRequested(SpirvInstruction *position,
                                        SourceLocation loc) {

tools/clang/lib/SPIRV/DeclResultIdMapper.h

@@ -516,11 +516,6 @@ public:
   bool writeBackOutputStream(const NamedDecl *decl, QualType type,
                              SpirvInstruction *value, SourceRange range = {});
 
-  /// \brief Negates to get the additive inverse of SV_Position.y if requested.
-  SpirvInstruction *invertYIfRequested(SpirvInstruction *position,
-                                       SourceLocation loc,
-                                       SourceRange range = {});
-
   /// \brief Reciprocates to get the multiplicative inverse of SV_Position.w
   /// if requested.
   SpirvInstruction *invertWIfRequested(SpirvInstruction *position,

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -594,8 +594,8 @@ SpirvEmitter::SpirvEmitter(CompilerInstance &ci)
     emitError("unknown shader module: %0", {}) << shaderModel->GetName();
 
   if (spirvOptions.invertY && !shaderModel->IsVS() && !shaderModel->IsDS() &&
-      !shaderModel->IsGS())
-    emitError("-fvk-invert-y can only be used in VS/DS/GS", {});
+      !shaderModel->IsGS() && !shaderModel->IsMS())
+    emitError("-fvk-invert-y can only be used in VS/DS/GS/MS", {});
 
   if (spirvOptions.useGlLayout && spirvOptions.useDxLayout)
     emitError("cannot specify both -fvk-use-dx-layout and -fvk-use-gl-layout",
@@ -7933,6 +7933,9 @@ void SpirvEmitter::assignToMSOutAttribute(
     valueType = astContext.UnsignedIntTy;
   }
   varInstr = spvBuilder.createAccessChain(valueType, varInstr, indices, loc);
+  if (semanticInfo.semantic->GetKind() == hlsl::Semantic::Kind::Position)
+    value = invertYIfRequested(value, semanticInfo.loc);
+
   spvBuilder.createStore(varInstr, value, loc);
 }
 
@@ -14327,6 +14330,22 @@ SpirvEmitter::createSpirvIntrInstExt(llvm::ArrayRef<const Attr *> attrs,
   return retVal;
 }
 
+SpirvInstruction *SpirvEmitter::invertYIfRequested(SpirvInstruction *position,
+                                                   SourceLocation loc,
+                                                   SourceRange range) {
+  // Negate SV_Position.y if requested
+  if (spirvOptions.invertY) {
+    const auto oldY = spvBuilder.createCompositeExtract(
+        astContext.FloatTy, position, {1}, loc, range);
+    const auto newY = spvBuilder.createUnaryOp(
+        spv::Op::OpFNegate, astContext.FloatTy, oldY, loc, range);
+    position = spvBuilder.createCompositeInsert(
+        astContext.getExtVectorType(astContext.FloatTy, 4), position, {1}, newY,
+        loc, range);
+  }
+  return position;
+}
+
 SpirvInstruction *
 SpirvEmitter::processSpvIntrinsicCallExpr(const CallExpr *expr) {
   const auto *funcDecl = expr->getDirectCallee();

tools/clang/lib/SPIRV/SpirvEmitter.h

@@ -114,6 +114,11 @@ public:
                          llvm::ArrayRef<SpirvInstruction *> spvArgs,
                          bool isInstr, SourceLocation loc);
 
+  /// \brief Negates to get the additive inverse of SV_Position.y if requested.
+  SpirvInstruction *invertYIfRequested(SpirvInstruction *position,
+                                       SourceLocation loc,
+                                       SourceRange range = {});
+
 private:
   void doFunctionDecl(const FunctionDecl *decl);
   void doVarDecl(const VarDecl *decl);

tools/clang/test/CodeGenSPIRV/mesh.invert.y.hlsl

@@ -0,0 +1,34 @@
+// RUN: %dxc -T ms_6_5 -E main -fcgl  %s -spirv -fvk-invert-y | FileCheck %s -check-prefix=CHECK -check-prefix=INVERT
+// RUN: %dxc -T ms_6_5 -E main -fcgl  %s -spirv | FileCheck %s -check-prefix=CHECK -check-prefix=NINVERT
+
+struct MeshPerVertex {
+    float4 position : SV_Position;
+};
+
+#define NUM_THREADS 128
+#define MAX_VERT 256
+#define MAX_PRIM 256
+
+// CHECK: [[v:%[0-9]+]] = OpConstantComposite %v4float %float_4 %float_5 %float_6 %float_7
+
+[outputtopology("point")]
+[numthreads(NUM_THREADS, 1, 1)]
+void main(out vertices MeshPerVertex verts[MAX_VERT],
+          out indices uint primitiveInd[MAX_PRIM],
+          in uint tid : SV_DispatchThreadID)
+{
+
+    SetMeshOutputCounts(MAX_VERT, MAX_PRIM);
+
+// CHECK: [[glPosition:%[0-9]+]] = OpAccessChain %_ptr_Output_v4float %gl_Position %47
+// NINVERT: OpStore [[glPosition]] [[v]]
+
+// INVERT: [[vy:%[0-9]+]] = OpCompositeExtract %float [[v]] 1
+// INVERT: [[nvy:%[0-9]+]] = OpFNegate %float [[vy]]
+// INVERT: [[nv:%[0-9]+]] = OpCompositeInsert %v4float [[nvy]] [[v]] 1
+// INVERT: OpStore [[glPosition]] [[nv]]
+    verts[tid].position = float4(4.0,5.0,6.0,7.0);
+
+    primitiveInd[6] = 2;
+}
+