[clang] [llvm] [HLSL][DXIL] Implement `refract` intrinsic (PR #147342)

[Farzon Lotfi via llvm-commits]

================
@@ -71,6 +71,42 @@ constexpr vector<T, L> reflect_vec_impl(vector<T, L> I, vector<T, L> N) {
 #endif
 }
 
+template <typename T> constexpr T refract_impl(T I, T N, T Eta) {
+  T Mul = N * I;
+  T K = 1 - Eta * Eta * (1 - (Mul * Mul));
+  T Result = (Eta * I - (Eta * Mul + sqrt(K)) * N);
+  return select<T>(K < 0, static_cast<T>(0), Result);
+}
+
+template <typename T, typename U>
+constexpr T refract_vec_impl(T I, T N, U Eta) {
+#if (__has_builtin(__builtin_spirv_refract))
+  if (is_vector<T>::value) {
+    return __builtin_spirv_refract(I, N, Eta);
+  }
+#else
+  T Mul = dot(N, I);
+  T K = 1 - Eta * Eta * (1 - Mul * Mul);
+  T Result = (Eta * I - (Eta * Mul + sqrt(K)) * N);
+  return select<T>(K < 0, static_cast<T>(0), Result);
+#endif
+}
----------------
farzonl wrote:

```suggestion
template <typename T, typename U>
constexpr T refract_impl(T I, T N, U Eta) {
#if (__has_builtin(__builtin_spirv_refract))
  if (is_vector<T>::value)
    return __builtin_spirv_refract(I, N, Eta);
#endif
  T Mul = dot(N, I);
  T K = 1 - Eta * Eta * (1 - Mul * Mul);
  T Result = (Eta * I - (Eta * Mul + sqrt(K)) * N);
  return select<T>(K < 0, static_cast<T>(0), Result);
}
```

https://github.com/llvm/llvm-project/pull/147342