[clang] [llvm] [HLSL] Implement the `smoothstep` intrinsic (PR #132288)

[Kaitlin Peng via llvm-commits]

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@@ -101,6 +101,44 @@ bool SemaSPIRV::CheckSPIRVBuiltinFunctionCall(unsigned BuiltinID,
     TheCall->setType(RetTy);
     break;
   }
+  case SPIRV::BI__builtin_spirv_smoothstep: {
+    if (SemaRef.checkArgCount(TheCall, 3))
+      return true;
+
+    ExprResult A = TheCall->getArg(0);
+    QualType ArgTyA = A.get()->getType();
+    auto *VTyA = ArgTyA->getAs<VectorType>();
+    if (!(ArgTyA->isScalarType() || VTyA)) {
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kmpeng wrote:

Would using `SemaRef.BuiltinElementwiseTernaryMath` with `ArgTyRestr=Sema::EltwiseBuiltinArgTyRestriction::FloatTy` be appropriate here for the first check?

https://github.com/llvm/llvm-project/pull/132288