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

[Kaitlin Peng via llvm-commits]

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@@ -322,5 +322,53 @@ reflect(__detail::HLSL_FIXED_VECTOR<float, L> I,
         __detail::HLSL_FIXED_VECTOR<float, L> N) {
   return __detail::reflect_vec_impl(I, N);
 }
+
+//===----------------------------------------------------------------------===//
+// smoothstep builtin
+//===----------------------------------------------------------------------===//
+
+/// \fn T smoothstep(T Min, T Max, T X)
+/// \brief Returns a smooth Hermite interpolation between 0 and 1, if \a X is in
+/// the range [\a Min, \a Max].
+/// \param Min The minimum range of the x parameter.
+/// \param Max The maximum range of the x parameter.
+/// \param X The specified value to be interpolated.
+///
+/// The return value is 0.0 if \a X ≤ \a Min and 1.0 if \a X ≥ \a Max. When \a
+/// Min < \a X < \a Max, the function performs smooth Hermite interpolation
+/// between 0 and 1.
+
+template <typename T>
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+const inline __detail::enable_if_t<__detail::is_arithmetic<T>::Value &&
+                                       __detail::is_same<half, T>::value,
+                                   T> smoothstep(T Min, T Max, T X) {
+  return __detail::smoothstep_impl(Min, Max, X);
+}
+
+template <typename T>
+const inline __detail::enable_if_t<
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kmpeng wrote:

I'm not sure how to do this when clang-format is an automatic process. The other intrinsics are also formatted the same way as mine.

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