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

[Farzon Lotfi via llvm-commits]

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@@ -25,3 +25,9 @@ def SPIRVReflect : Builtin {
   let Attributes = [NoThrow, Const];
   let Prototype = "void(...)";
 }
+
+def SPIRVSmoothStep : Builtin {
+  let Spellings = ["__builtin_spirv_smoothstep"];
+  let Attributes = [NoThrow, Const];
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farzonl wrote:

do we need `CustomeTypeChecking`?

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