[SPIR-V] Fix mesh payload global variable for VK_EXT_mesh_shaders (#6526)

The existing logic from `VK_NV_mesh_shader` was incorrectly adapted for
the `VK_EXT_mesh_shader` implementation when it comes to the handling of
payloads as in/out variables. Because `TaskPayloadWorkgroupEXT` must be
applied to a single global `OpVariable` for each task/mesh shader, the
struct should not be flattened. Further, Location assignment is not
necessary for these input and output variables, so the usual reason for
flattening structs does not apply.

This change now removes the inner struct member global variables and
ensures the parent payload is decorated with `TaskPayloadWorkgroupEXT`.
Note that for amplification/task shaders, the payload variable is
created with the `groupshared` decl, and then its storage class needs to
be updated when that variable is used as a parameter to the
`DispatchMesh` call, as described in:
https://docs.vulkan.org/spec/latest/proposals/proposals/VK_EXT_mesh_shader.html#_hlsl_changes

Tested with new validation checks from:
KhronosGroup/SPIRV-Tools#5640

Fixes #5981

Author: sudonatalie

tools/clang/lib/SPIRV/DeclResultIdMapper.cpp

@@ -3582,32 +3582,61 @@ bool DeclResultIdMapper::createPayloadStageVars(
   }
 
   const auto loc = decl->getLocation();
-  if (!type->isStructureType()) {
-    StageVar stageVar(sigPoint, /*semaInfo=*/{}, /*builtinAttr=*/nullptr, type,
-                      getLocationAndComponentCount(astContext, type));
-    const auto name = namePrefix.str() + "." + decl->getNameAsString();
-    SpirvVariable *varInstr = spvBuilder.addStageIOVar(
-        type, sc, name, /*isPrecise=*/false, /*isNointerp=*/false, loc);
-
-    if (!varInstr)
-      return false;
 
-    // Even though these as user defined IO stage variables, set them as SPIR-V
-    // builtins in order to bypass any semantic string checks and location
-    // assignment.
-    stageVar.setIsSpirvBuiltin();
-    stageVar.setSpirvInstr(varInstr);
-    if (stageVar.getStorageClass() == spv::StorageClass::Input ||
-        stageVar.getStorageClass() == spv::StorageClass::Output) {
-      stageVar.setEntryPoint(entryFunction);
+  // Most struct type stage vars must be flattened, but for EXT_mesh_shaders the
+  // mesh payload struct should be decorated with TaskPayloadWorkgroupEXT and
+  // used directly as the OpEntryPoint variable.
+  if (!type->isStructureType() ||
+      featureManager.isExtensionEnabled(Extension::EXT_mesh_shader)) {
+
+    SpirvVariable *varInstr = nullptr;
+
+    // Check whether a mesh payload module variable has already been added, as
+    // is the case for the groupshared payload variable parameter of
+    // DispatchMesh. In this case, change the storage class from Workgroup to
+    // TaskPayloadWorkgroupEXT.
+    if (featureManager.isExtensionEnabled(Extension::EXT_mesh_shader)) {
+      for (SpirvVariable *moduleVar : spvBuilder.getModule()->getVariables()) {
+        if (moduleVar->getAstResultType() == type) {
+          moduleVar->setStorageClass(
+              spv::StorageClass::TaskPayloadWorkgroupEXT);
+          varInstr = moduleVar;
+        }
+      }
     }
-    stageVars.push_back(stageVar);
 
-    if (!featureManager.isExtensionEnabled(Extension::EXT_mesh_shader)) {
-      // Decorate with PerTaskNV for mesh/amplification shader payload
-      // variables.
-      spvBuilder.decoratePerTaskNV(varInstr, payloadMemOffset,
-                                   varInstr->getSourceLocation());
+    // If necessary, create new stage variable for mesh payload.
+    if (!varInstr) {
+      LocationAndComponent locationAndComponentCount =
+          type->isStructureType()
+              ? LocationAndComponent({0, 0, false})
+              : getLocationAndComponentCount(astContext, type);
+      StageVar stageVar(sigPoint, /*semaInfo=*/{}, /*builtinAttr=*/nullptr,
+                        type, locationAndComponentCount);
+      const auto name = namePrefix.str() + "." + decl->getNameAsString();
+      varInstr = spvBuilder.addStageIOVar(type, sc, name, /*isPrecise=*/false,
+                                          /*isNointerp=*/false, loc);
+
+      if (!varInstr)
+        return false;
+
+      // Even though these as user defined IO stage variables, set them as
+      // SPIR-V builtins in order to bypass any semantic string checks and
+      // location assignment.
+      stageVar.setIsSpirvBuiltin();
+      stageVar.setSpirvInstr(varInstr);
+      if (stageVar.getStorageClass() == spv::StorageClass::Input ||
+          stageVar.getStorageClass() == spv::StorageClass::Output) {
+        stageVar.setEntryPoint(entryFunction);
+      }
+      stageVars.push_back(stageVar);
+
+      if (!featureManager.isExtensionEnabled(Extension::EXT_mesh_shader)) {
+        // Decorate with PerTaskNV for mesh/amplification shader payload
+        // variables.
+        spvBuilder.decoratePerTaskNV(varInstr, payloadMemOffset,
+                                     varInstr->getSourceLocation());
+      }
     }
 
     if (asInput) {

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

@@ -1,7 +1,7 @@
 // RUN: %dxc -T as_6_5 -fspv-target-env=vulkan1.1spirv1.4 -E main -fcgl  %s -spirv | FileCheck %s
 // CHECK:  OpCapability MeshShadingEXT
 // CHECK:  OpExtension "SPV_EXT_mesh_shader"
-// CHECK:  OpEntryPoint TaskEXT %main "main" [[drawid:%[0-9]+]] %gl_LocalInvocationID %gl_WorkGroupID %gl_GlobalInvocationID %gl_LocalInvocationIndex %out_var_dummy %out_var_pos
+// CHECK:  OpEntryPoint TaskEXT %main "main" [[drawid:%[0-9]+]] %gl_LocalInvocationID %gl_WorkGroupID %gl_GlobalInvocationID %gl_LocalInvocationIndex %pld
 // CHECK:  OpExecutionMode %main LocalSize 128 1 1
 
 // CHECK:  OpDecorate [[drawid]] BuiltIn DrawIndex
@@ -11,14 +11,12 @@
 // CHECK:  OpDecorate %gl_LocalInvocationIndex BuiltIn LocalInvocationIndex
 
 
-// CHECK:  %pld = OpVariable %_ptr_Workgroup_MeshPayload Workgroup
+// CHECK:  %pld = OpVariable %_ptr_TaskPayloadWorkgroupEXT_MeshPayload TaskPayloadWorkgroupEXT
 // CHECK:  [[drawid]] = OpVariable %_ptr_Input_int Input
 // CHECK:  %gl_LocalInvocationID = OpVariable %_ptr_Input_v3uint Input
 // CHECK:  %gl_WorkGroupID = OpVariable %_ptr_Input_v3uint Input
 // CHECK:  %gl_GlobalInvocationID = OpVariable %_ptr_Input_v3uint Input
 // CHECK:  %gl_LocalInvocationIndex = OpVariable %_ptr_Input_uint Input
-// CHECK:  %out_var_dummy = OpVariable %_ptr_TaskPayloadWorkgroupEXT__arr_float_uint_10 TaskPayloadWorkgroupEXT
-// CHECK:  %out_var_pos = OpVariable %_ptr_TaskPayloadWorkgroupEXT_v4float TaskPayloadWorkgroupEXT
 struct MeshPayload {
     float dummy[10];
     float4 pos;
@@ -47,16 +45,12 @@ void main(
 // CHECK:  %tid = OpFunctionParameter %_ptr_Function_uint
 // CHECK:  %tig = OpFunctionParameter %_ptr_Function_uint
 // 
-// CHECK:  [[a:%[0-9]+]] = OpAccessChain %_ptr_Workgroup_v4float %pld %int_1
+// CHECK:  [[a:%[0-9]+]] = OpAccessChain %_ptr_TaskPayloadWorkgroupEXT_v4float %pld %int_1
 // CHECK:  OpStore [[a]] {{%[0-9]+}}
     pld.pos = float4(gtid.x, gid.y, tid, tig);
 
 // CHECK:  OpControlBarrier %uint_2 %uint_2 %uint_264
 // CHECK:  [[e:%[0-9]+]] = OpLoad %MeshPayload %pld
-// CHECK:  [[f:%[0-9]+]] = OpCompositeExtract %_arr_float_uint_10 [[e]] 0
-// CHECK:  OpStore %out_var_dummy [[f]]
-// CHECK:  [[g:%[0-9]+]] = OpCompositeExtract %v4float [[e]] 1
-// CHECK:  OpStore %out_var_pos [[g]]
 // CHECK:  [[h:%[0-9]+]] = OpLoad %int %drawId
 // CHECK:  [[i:%[0-9]+]] = OpBitcast %uint [[h]]
 // CHECK:  [[j:%[0-9]+]] = OpLoad %int %drawId

tools/clang/test/CodeGenSPIRV/meshshading.ext.triangle.mesh.hlsl

@@ -1,7 +1,7 @@
 // RUN: %dxc -T ms_6_5 -fspv-target-env=universal1.5 -E main -fcgl  %s -spirv | FileCheck %s
 // CHECK:  OpCapability MeshShadingEXT
 // CHECK:  OpExtension "SPV_EXT_mesh_shader"
-// CHECK:  OpEntryPoint MeshEXT %main "main" %gl_ClipDistance %gl_CullDistance %in_var_dummy %in_var_pos [[drawid:%[0-9]+]] %gl_LocalInvocationID %gl_WorkGroupID %gl_GlobalInvocationID %gl_LocalInvocationIndex %gl_Position %gl_PointSize %out_var_USER %out_var_USER_ARR %out_var_USER_MAT [[primindices:%[0-9]+]] %gl_PrimitiveID %gl_Layer %gl_ViewportIndex [[cullprim:%[0-9]+]] [[primshadingrate:%[0-9]+]] %out_var_PRIM_USER %out_var_PRIM_USER_ARR 
+// CHECK:  OpEntryPoint MeshEXT %main "main" %gl_ClipDistance %gl_CullDistance %in_var_pld [[drawid:%[0-9]+]] %gl_LocalInvocationID %gl_WorkGroupID %gl_GlobalInvocationID %gl_LocalInvocationIndex %gl_Position %gl_PointSize %out_var_USER %out_var_USER_ARR %out_var_USER_MAT [[primindices:%[0-9]+]] %gl_PrimitiveID %gl_Layer %gl_ViewportIndex [[cullprim:%[0-9]+]] [[primshadingrate:%[0-9]+]] %out_var_PRIM_USER %out_var_PRIM_USER_ARR
 // CHECK:  OpExecutionMode %main LocalSize 128 1 1
 // CHECK:  OpExecutionMode %main OutputTrianglesNV
 // CHECK:  OpExecutionMode %main OutputVertices 64
@@ -37,8 +37,7 @@
 
 // CHECK:  %gl_ClipDistance = OpVariable %_ptr_Output__arr__arr_float_uint_5_uint_64 Output
 // CHECK:  %gl_CullDistance = OpVariable %_ptr_Output__arr__arr_float_uint_3_uint_64 Output
-// CHECK:  %in_var_dummy = OpVariable %_ptr_TaskPayloadWorkgroupEXT__arr_float_uint_10 TaskPayloadWorkgroupEXT
-// CHECK:  %in_var_pos = OpVariable %_ptr_TaskPayloadWorkgroupEXT_v4float TaskPayloadWorkgroupEXT
+// CHECK:  %in_var_pld = OpVariable %_ptr_TaskPayloadWorkgroupEXT_MeshPayload TaskPayloadWorkgroupEXT
 // CHECK:  %gl_GlobalInvocationID = OpVariable %_ptr_Input_v3uint Input
 // CHECK:  %gl_LocalInvocationIndex = OpVariable %_ptr_Input_uint Input
 // CHECK:  %gl_Position = OpVariable %_ptr_Output__arr_v4float_uint_64 Output