[Diag] Diagnose missing numthreads in compute shaders

Currently we error out in validation if a compute shader doesn't have
a numthreads attribute:

```
<source>:2: error: Declared Thread Group X size 2833376888 outside valid range [1..1024].
<source>:2: error: Declared Thread Group Y size 21956 outside valid range [1..1024].
<source>:2: error: Declared Thread Group Z size 2833381336 outside valid range [1..64].
<source>:2: error: Declared Thread Group Count 3863291136 (X*Y*Z) is beyond the valid maximum of 1024.
```

Instead, diagnose this in Sema like we do for mesh and amplitude shaders

Reviewers: damyanp, bob80905, pow2clk, llvm-beanz

Reviewed By: llvm-beanz, bob80905, damyanp, pow2clk

Pull Request: microsoft#6021

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -12584,19 +12584,12 @@ void SpirvEmitter::processPixelShaderAttributes(const FunctionDecl *decl) {
 }
 
 void SpirvEmitter::processComputeShaderAttributes(const FunctionDecl *decl) {
-  // If not explicitly specified, x, y, and z should be defaulted to 1.
-  uint32_t x = 1, y = 1, z = 1;
+  auto *numThreadsAttr = decl->getAttr<HLSLNumThreadsAttr>();
+  assert(numThreadsAttr && "thread group size missing from entry-point");
 
-  if (auto *numThreadsAttr = decl->getAttr<HLSLNumThreadsAttr>()) {
-    x = static_cast<uint32_t>(numThreadsAttr->getX());
-    y = static_cast<uint32_t>(numThreadsAttr->getY());
-    z = static_cast<uint32_t>(numThreadsAttr->getZ());
-  } else {
-    emitError("thread group size [numthreads(x,y,z)] is missing from the "
-              "entry-point function",
-              decl->getLocation());
-    return;
-  }
+  uint32_t x = static_cast<uint32_t>(numThreadsAttr->getX());
+  uint32_t y = static_cast<uint32_t>(numThreadsAttr->getY());
+  uint32_t z = static_cast<uint32_t>(numThreadsAttr->getZ());
 
   spvBuilder.addExecutionMode(entryFunction, spv::ExecutionMode::LocalSize,
                               {x, y, z}, decl->getLocation());

tools/clang/lib/Sema/SemaHLSL.cpp

@@ -15425,6 +15425,9 @@ void DiagnoseGeometryEntry(Sema &S, FunctionDecl *FD,
 void DiagnoseComputeEntry(Sema &S, FunctionDecl *FD, llvm::StringRef StageName,
                           bool isActiveEntry) {
   if (isActiveEntry) {
+    if (!(FD->getAttr<HLSLNumThreadsAttr>()))
+      S.Diags.Report(FD->getLocation(), diag::err_hlsl_missing_attr)
+          << StageName << "numthreads";
     if (auto WaveSizeAttr = FD->getAttr<HLSLWaveSizeAttr>()) {
       std::string profile = S.getLangOpts().HLSLProfile;
       const ShaderModel *SM = hlsl::ShaderModel::GetByName(profile.c_str());

tools/clang/test/CodeGenSPIRV_Lit/attribute.numthreads.lib.missing.hlsl

@@ -6,9 +6,8 @@ void entryHistogram(uint3 id: SV_DispatchThreadID, uint idx: SV_GroupIndex)
 {
 }
 
-// CHECK: 11:6: error: thread group size [numthreads(x,y,z)] is missing from the entry-point function
+// CHECK: 11:6: error: compute entry point must have the numthreads attribute
 [shader("compute")]
 void entryAverage(uint3 id: SV_DispatchThreadID, uint idx: SV_GroupIndex)
 {
 }
-

tools/clang/test/CodeGenSPIRV_Lit/attribute.numthreads.missing.hlsl

@@ -1,4 +1,4 @@
 // RUN: not %dxc -T cs_6_0 -E main -fcgl  %s -spirv  2>&1 | FileCheck %s
 
-// CHECK: 4:6: error: thread group size [numthreads(x,y,z)] is missing from the entry-point function
+// CHECK: 4:6: error: compute entry point must have the numthreads attribute
 void main() {}

tools/clang/test/SemaHLSL/attributes/NecessaryAttribsInLib.hlsl

@@ -55,3 +55,7 @@ void MSmain(out vertices myvert verts[32],
   myvert v = {0.0, 0.0, 0.0, 0.0};
   verts[ix] = v;
 }
+
+// expected-error@+2{{compute entry point must have the numthreads attribute}}
+[shader("compute")]
+void CSmain() {}