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

[Farzon Lotfi via llvm-commits]

================
@@ -101,6 +101,52 @@ bool SemaSPIRV::CheckSPIRVBuiltinFunctionCall(unsigned BuiltinID,
     TheCall->setType(RetTy);
     break;
   }
+  case SPIRV::BI__builtin_spirv_smoothstep: {
+    if (SemaRef.checkArgCount(TheCall, 3))
+      return true;
+
+    // check if the all arguments have floating representation
+    ExprResult A = TheCall->getArg(0);
+    QualType ArgTyA = A.get()->getType();
+    if (!ArgTyA->hasFloatingRepresentation()) {
+      SemaRef.Diag(A.get()->getBeginLoc(),
+                   diag::err_typecheck_convert_incompatible)
----------------
farzonl wrote:

I think @spall is working on a change that might edit `err_builtin_invalid_arg_type` to include matricies at some point as a  diagnostic argument. For now since we don't have matrix support I think this is fine.

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