The Haskell assembly is using the 3-op AVX instructions, but not 256bit registers. The example is simple enough that it may not make a difference (2-op vs 3-op

The Haskell assembly is using the 3-op AVX instructions, but not 256bit registers. The example is simple enough that it may not make a difference (2-op vs 3-op instructions), but in a more complex function with register spills it could have. ("-mavx" should be enough). all that said, it is still very impressive work!