[clang] [HLSL] Implement SV_GroupThreadId semantic (PR #117781)

[Zhengxing li via cfe-commits]

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@@ -2,15 +2,18 @@
 // RUN: %clang_cc1 -triple dxil-pc-shadermodel6.0-mesh -hlsl-entry CSMain -x hlsl -finclude-default-header  -verify -o - %s
 
 [numthreads(8,8,1)]
-// expected-error at +3 {{attribute 'SV_GroupIndex' is unsupported in 'mesh' shaders, requires compute}}
-// expected-error at +2 {{attribute 'SV_DispatchThreadID' is unsupported in 'mesh' shaders, requires compute}}
-// expected-error at +1 {{attribute 'SV_GroupID' is unsupported in 'mesh' shaders, requires compute}}
-void CSMain(int GI : SV_GroupIndex, uint ID : SV_DispatchThreadID, uint GID : SV_GroupID) {
-// CHECK: FunctionDecl 0x{{[0-9a-fA-F]+}} <{{.*}}> line:[[@LINE-1]]:6 CSMain 'void (int, uint, uint)'
+// expected-error at +4 {{attribute 'SV_GroupIndex' is unsupported in 'mesh' shaders, requires compute}}
+// expected-error at +3 {{attribute 'SV_DispatchThreadID' is unsupported in 'mesh' shaders, requires compute}}
+// expected-error at +2 {{attribute 'SV_GroupID' is unsupported in 'mesh' shaders, requires compute}}
+// expected-error at +1 {{attribute 'SV_GroupThreadID' is unsupported in 'mesh' shaders, requires compute}}
+void CSMain(int GI : SV_GroupIndex, uint ID : SV_DispatchThreadID, uint GID : SV_GroupID, uint GThreadID : SV_GroupThreadID) {
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lizhengxing wrote:

@tex3d  Yes, you're right. I checked the spec https://microsoft.github.io/DirectX-Specs/d3d/MeshShader.html .  Those 4 attributes are legal for the mesh shader.

I think that they are legal for the amplification shader as well.

It looks like that we did something wrong in `SemaHLSL::CheckSemanticAnnotation` function
```
  switch (AnnotationAttr->getKind()) {
  case attr::HLSLSV_DispatchThreadID:
  case attr::HLSLSV_GroupIndex:
  case attr::HLSLSV_GroupThreadID:
  case attr::HLSLSV_GroupID:
    if (ST == llvm::Triple::Compute)
      return;
    DiagnoseAttrStageMismatch(AnnotationAttr, ST, {llvm::Triple::Compute});
    break;
```
We only check `Compute Shader` triple. I think that we should add checks for  `Mesh Shader` and `Amplification Shader` triples here. Right?

https://github.com/llvm/llvm-project/pull/117781