[PATCH] D20598: [X86] Detect SAD patterns and emit psadbw instructions on X86 redux

[Wei Mi via llvm-commits]

> Regarding the shuffle - I don't see a good way to get rid of it locally. If you have an idea on how to do that, I'll be happy to hear it.

Can we use TRUNCATE instead? SadVT is 2xi64, truncate it to 2xi32.

    if (VT.getSizeInBits() < ResVT.getSizeInBits()) {
      MVT ResVT = MVT::getVectorVT(MVT::i32, VT.getSizeInBits() / 32);
      Sad = DAG.getNode(ISD::TRUNCATE, DL, ResVT, SadVT);
    }