[clang] [llvm] [HLSL][DXIL] Implement `refract` intrinsic (PR #136026)

[Farzon Lotfi via cfe-commits]

================
@@ -71,6 +71,27 @@ 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 k = 1 - eta * eta * (1 - (N * I * N *I));
+  if(k < 0)
----------------
farzonl wrote:

I feel like we can simplify these conditionals to use a select instead.

https://github.com/llvm/llvm-project/pull/136026