[clang] [HLSL] Implement the dst HLSL Function (PR #133828)

[via cfe-commits]

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@@ -174,6 +174,31 @@ const inline float distance(__detail::HLSL_FIXED_VECTOR<float, N> X,
                             __detail::HLSL_FIXED_VECTOR<float, N> Y) {
   return __detail::distance_vec_impl(X, Y);
 }
+//===----------------------------------------------------------------------===//
+// dst builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn fvector dst( fvector, fvector)
+/// \brief Returns the length of a vector
+/// \param Src0 [in] The first vector contain {_, d*d, d*d, _}
+/// \param Src1 [in] The second vector contain {_, 1/d, _, 1/d}
+///
+/// Return the computed distance vector contain {1, d, d*d, 1/d}
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metkarpoonam wrote:

The combination of squared distance (src0) and reciprocal distance (src1) enables the dst function to efficiently compute a distance vector.
dest = (1, d*d, d*d, 1) * (1, 1/d, 1, 1/d);
dest = (1, d, d*d, 1/d)

https://stackoverflow.com/questions/8525803/what-is-the-hlsl-dst-instruction-for

https://github.com/llvm/llvm-project/pull/133828