[clang] [llvm] [HLSL] Implement the `faceforward` intrinsic (PR #135878)

[Finn Plummer via llvm-commits]

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@@ -214,6 +214,53 @@ const inline double4 dst(double4 Src0, double4 Src1) {
   return __detail::dst_impl(Src0, Src1);
 }
 
+//===----------------------------------------------------------------------===//
+// faceforward builtin
+//===----------------------------------------------------------------------===//
+
+/// \fn T faceforward(T N, T I, T Ng)
+/// \brief Flips the surface-normal (if needed) to face in a direction opposite
+/// to \a I. Returns the result in \a N.
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inbelic wrote:

I assume this is copied from the docs, but "returns the result in N" is quite confusing to me. Maybe it was meant to be "Returns the result in terms of N" or the like?

https://github.com/llvm/llvm-project/pull/135878