Latest DXC requires a new keyword [raypayload] on a struct when used as ray-tracing payload

[jkwak-work]

When using the latest DXC binary, we are failing on two existing tests,

gfx-unit-test-tool/RayTracingTestAD3D12.internal
gfx-unit-test-tool/RayTracingTestBD3D12.internal

This failure is observed on the CI testing of PR 6095.

Reproduce step
It can be reproduced with the following command,

$ build/Release/bin/slang-test.exe gfx-unit-test-tool/RayTracingTestBD3D12
Supported backends: fxc dxc glslang spirv-dis clang visualstudio genericcpp nvrtc llvm spirv-opt metal tint
error: !SLANG_FAILED(loadShaderProgram(device, rayTracingProgram.writeRef())) - D:\sbf\git\slang\test_server_should_use_a_custom_d3d12core_dll\tools\gfx-unit-test\ray-tracing-tests.cpp (363)
FAILED test: 'gfx-unit-test-tool/RayTracingTestBD3D12.internal'
0% of tests passed (0/1)
failing tests:
---
gfx-unit-test-tool/RayTracingTestBD3D12.internal
---

Error message
The real error message can be seen only with a debugger and it says,

dxc 1.7: tools/gfx-unit-test/ray-tracing-test-shaders.slang(26): error :  type 'RayPayload_0' used as payload requires that it is annotated with the [raypayload] attribute
dxc 1.7: note :     RayPayload_0 payload_0;
dxc 1.7: note :                  ^

This seems to be a new requirement given that the shader was working fine before.
DXC document states the following,

Syntax
Any structure type used as payload must carry the [raypayload] type attribute as part of the type declaration as follows:
struct [raypayload] MyPayload{ ... };

Goal
The goal is to add [raypayload] attribute to any struct that is used as a ray-tracing payload when targeting HLSL.
Currently the testing shader is translated into HLSL without the keyword,

build/Release/bin/slangc.exe -target hlsl -stage raygeneration -entry rayGenShaderA tools/gfx-unit-test/ray-tracing-test-shaders.slang

RaytracingAccelerationStructure sceneBVH_0 : register(t0);

RWTexture2D<float4 > resultTexture_0 : register(u0);

struct RayPayload_0
{
    float4 color_0;
};

[shader("raygeneration")]void rayGenShaderA()
{
    uint3 _S1 = DispatchRaysIndex();
......
    RayPayload_0 payload_0;
......
}

The line struct RayPayload_0 should have [raypayload] attribute when the issue is fixed.

[skallweitNV]

I also just stumbled over this with dxc 1.8

[jkwak-work]

It seems that GLSL and SPIRV target uses [__vulkanRayPayload].
For HLSL target, it seems like the payload always goes through a function,

__generic<T>
__intrinsic_op($(kIROp_ForceVarIntoStructTemporarily))
Ref<T> __forceVarIntoStructTemporarily(inout T maybeStruct);

I am guessing the function should emit [RayPayload] attribute when synthesize a struct.
And it will need to legalize if the parameter was already a struct.