Use const ref for mesh payload (#3254)

* Use const ref for mesh payload

* Test mesh payload hlsl output

2 files changed, 9 insertions, 7 deletions

diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 09992fb14..065263a59 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -2527,19 +2527,17 @@ void addCallArgsForParam(
     /// Compute the direction for a parameter based on its declaration
 ParameterDirection getParameterDirection(VarDeclBase* paramDecl)
 {
-    if( paramDecl->hasModifier<RefModifier>()
+    if( paramDecl->hasModifier<RefModifier>())
+    {
+        return kParameterDirection_Ref;
+    }
+    if (paramDecl->hasModifier<ConstRefModifier>()
         || paramDecl->hasModifier<HLSLPayloadModifier>() )
     {
-        // The AST specified `ref` or `payload`:
-
         // The payload types are a groupshared variable, and we really don't
         // want to copy that into registers in every invocation on platforms
         // where this matters, so treat them as by-reference here.
 
-        return kParameterDirection_Ref;
-    }
-    if (paramDecl->hasModifier<ConstRefModifier>())
-    {
         return kParameterDirection_ConstRef;
     }
     if( paramDecl->hasModifier<InOutModifier>() )
diff --git a/tests/pipeline/rasterization/mesh/task-simple.slang b/tests/pipeline/rasterization/mesh/task-simple.slang
index 67bd729b1..58ec9a527 100644
--- a/tests/pipeline/rasterization/mesh/task-simple.slang
+++ b/tests/pipeline/rasterization/mesh/task-simple.slang
@@ -1,5 +1,6 @@
 //TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK): -task -output-using-type -dx12 -use-dxil -profile sm_6_6 -render-features mesh-shader
 //TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK): -task -output-using-type -vk -profile glsl_450+spirv_1_4 -render-features mesh-shader
+//TEST:SIMPLE(filecheck=HLSL):-target hlsl -entry meshMain -stage mesh
 
 // To test a simple mesh shader, we'll generate 4 triangles, the vertices of
 // each one will hold the triangle index and a value (the square). The fragment
@@ -69,6 +70,9 @@ const static uint MAX_PRIMS = 4;
 void meshMain(
     in uint tig : SV_GroupIndex,
     in payload MeshPayload meshPayload,
+    // Check that we correctly generate the specific 'in payload' that HLSL
+    // requires:
+    // HLSL: , in payload MeshPayload
     out Vertices<Vertex, MAX_VERTS> verts,
     out Indices<uint3, MAX_PRIMS> triangles)
 {