[SPIRV] Cast SV_CULLPRIMITIVE to uint (microsoft#6297)

When SV_CULLPRIMITIVE is the output of a mesh shader, its type is
changed to uint because a Vulkan interface variable cannot be a bool.
However, we do not change the access to the variable to match.

This change will modify stores to the variable to be stores of a uint
instead of a bool.

Fixes microsoft#6042

Author: s-perron

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -7677,16 +7677,24 @@ void SpirvEmitter::assignToMSOutAttribute(
   assert(semanticInfo.isValid());
   const auto loc = decl->getLocation();
   // Special handle writes to clip/cull distance attributes.
-  if (!declIdMapper.glPerVertex.tryToAccess(
+  if (declIdMapper.glPerVertex.tryToAccess(
           hlsl::DXIL::SigPointKind::MSOut, semanticInfo.semantic->GetKind(),
           semanticInfo.index, attrIndex, &value, /*noWriteBack=*/false,
           vecComponent, loc)) {
-    // All other attribute writes are handled below.
-    auto *varInstr = declIdMapper.getStageVarInstruction(decl);
-    QualType valueType = value->getAstResultType();
-    varInstr = spvBuilder.createAccessChain(valueType, varInstr, indices, loc);
-    spvBuilder.createStore(varInstr, value, loc);
+    return;
   }
+
+  // All other attribute writes are handled below.
+  auto *varInstr = declIdMapper.getStageVarInstruction(decl);
+  QualType valueType = value->getAstResultType();
+  if (valueType->isBooleanType()) {
+    // Externally visible variables are changed to uint, so we need to cast the
+    // value to uint.
+    value = castToInt(value, valueType, astContext.UnsignedIntTy, loc);
+    valueType = astContext.UnsignedIntTy;
+  }
+  varInstr = spvBuilder.createAccessChain(valueType, varInstr, indices, loc);
+  spvBuilder.createStore(varInstr, value, loc);
 }
 
 void SpirvEmitter::assignToMSOutIndices(

tools/clang/test/CodeGenSPIRV/meshshading.ext.cullprimative.hlsl

@@ -0,0 +1,34 @@
+// RUN: %dxc -T ms_6_6 -fspv-target-env=vulkan1.1spirv1.4 -E main %s -spirv | FileCheck %s
+
+struct MeshletPrimitiveOut
+{
+	bool m_cullPrimitive : SV_CULLPRIMITIVE;
+};
+
+// m_cullPrimitive will have to be turned into a uint because of the Vulkan
+// specification says that externally visible variables cannot be bool.
+// CHECK: OpDecorate [[var:%[0-9]+]] BuiltIn CullPrimitiveEXT
+// CHECK: OpDecorate [[var]] PerPrimitiveNV
+// CHECK: [[var]] = OpVariable %_ptr_Output__arr_uint_uint_2 Output
+
+struct VertOut
+{
+    float4 m_svPosition : SV_POSITION;
+};
+
+#define SIZE 2
+
+[numthreads(SIZE, 1, 1)] [outputtopology("triangle")]
+void main(uint svGroupIndex : SV_GROUPINDEX, 
+    out vertices VertOut verts[SIZE], 
+    out indices uint3 indices[SIZE], 
+    out primitives MeshletPrimitiveOut primitives[SIZE])
+{
+    SetMeshOutputCounts(SIZE, SIZE);
+
+// Make sure that the references to m_cullPrimitive use uints.
+// CHECK: [[idx:%[0-9]+]] = OpLoad %uint %gl_LocalInvocationIndex
+// CHECK: [[ac:%[0-9]+]] = OpAccessChain %_ptr_Output_uint [[var]] [[idx]]
+// CHECK: OpStore [[ac]] %uint_0
+    primitives[svGroupIndex].m_cullPrimitive = false;
+}