Fix GroupSharedLimitASTest and GroupSharedLimitMSTest execution tests (#8351)

- Change Init="Zero" to Init="ByName" on UAVBuffer0 resources in
ShaderOpArith.xml so the C++ callback fires to set shader text and
resize the buffer.
- Update NumElements from 128 to 4096 on UAV descriptors to match the
4096 DWORDs the shaders write.
- Add dummy SV_Position write in mesh shaders to satisfy DXIL validation
requirement that all output semantics have stores.

Co-authored-by: Copilot <[email protected]>

Author: JoeCitizen

tools/clang/unittests/HLSLExec/ExecutionTest.cpp

@@ -10855,6 +10855,7 @@ void ExecutionTest::GroupSharedLimitASTest() {
                   out vertices MeshOutput verts[3],
                   out indices uint3 tris[1]) {
         SetMeshOutputCounts(0, 0);
+        verts[0].pos = float4(0, 0, 0, 0);
       }
 
       float4 PSMain() : SV_Target { return float4(0,0,0,0); }
@@ -10914,6 +10915,7 @@ void ExecutionTest::GroupSharedLimitMSTest() {
                   out vertices MeshOutput verts[3],
                   out indices uint3 tris[1]) {
         SetMeshOutputCounts(0, 0);
+        verts[0].pos = float4(0, 0, 0, 0);
         for (uint i = GI; i < GSM_DWORDS; i += 64)
           g_shared[i] = i;
         GroupMemoryBarrierWithGroupSync();

tools/clang/unittests/HLSLExec/ShaderOpArith.xml

@@ -1869,13 +1869,13 @@
           RootFlags(0),
           DescriptorTable(UAV(u0))
       </RootSignature>
-      <Resource Name="UAVBuffer0" Dimension="BUFFER" Width="512" InitialResourceState="COPY_DEST" Init="Zero" Flags="ALLOW_UNORDERED_ACCESS" TransitionTo="UNORDERED_ACCESS" ReadBack="true" />
+      <Resource Name="UAVBuffer0" Dimension="BUFFER" Width="512" InitialResourceState="COPY_DEST" Init="ByName" Flags="ALLOW_UNORDERED_ACCESS" TransitionTo="UNORDERED_ACCESS" ReadBack="true" />
       <Resource Name="RTarget" Dimension="TEXTURE2D" Width="4" Height="4" Format="R8G8B8A8_UNORM" Flags="ALLOW_RENDER_TARGET" InitialResourceState="COPY_DEST" ReadBack="false" />
       <RootValues>
           <RootValue HeapName="ResHeap" />
       </RootValues>
       <DescriptorHeap Name="ResHeap" Type="CBV_SRV_UAV">
-          <Descriptor Name="U0" Kind="UAV" ResName="UAVBuffer0" NumElements="128" StructureByteStride="4" />
+          <Descriptor Name="U0" Kind="UAV" ResName="UAVBuffer0" NumElements="4096" StructureByteStride="4" />
       </DescriptorHeap>
       <DescriptorHeap Name="RtvHeap" NumDescriptors="1" Type="RTV">
           <Descriptor Name="RTarget" Kind="RTV" />
@@ -1895,13 +1895,13 @@
           RootFlags(0),
           DescriptorTable(UAV(u0))
       </RootSignature>
-      <Resource Name="UAVBuffer0" Dimension="BUFFER" Width="512" InitialResourceState="COPY_DEST" Init="Zero" Flags="ALLOW_UNORDERED_ACCESS" TransitionTo="UNORDERED_ACCESS" ReadBack="true" />
+      <Resource Name="UAVBuffer0" Dimension="BUFFER" Width="512" InitialResourceState="COPY_DEST" Init="ByName" Flags="ALLOW_UNORDERED_ACCESS" TransitionTo="UNORDERED_ACCESS" ReadBack="true" />
       <Resource Name="RTarget" Dimension="TEXTURE2D" Width="4" Height="4" Format="R8G8B8A8_UNORM" Flags="ALLOW_RENDER_TARGET" InitialResourceState="COPY_DEST" ReadBack="false" />
       <RootValues>
           <RootValue HeapName="ResHeap" />
       </RootValues>
       <DescriptorHeap Name="ResHeap" Type="CBV_SRV_UAV">
-          <Descriptor Name="U0" Kind="UAV" ResName="UAVBuffer0" NumElements="128" StructureByteStride="4" />
+          <Descriptor Name="U0" Kind="UAV" ResName="UAVBuffer0" NumElements="4096" StructureByteStride="4" />
       </DescriptorHeap>
       <DescriptorHeap Name="RtvHeap" NumDescriptors="1" Type="RTV">
           <Descriptor Name="RTarget" Kind="RTV" />