//    broadcast_dimensions = dense<[$dimensions[0]]>},
//
// where $dimensions is of size 1. It ususally comes from an IotaOp that is
// folded to ConstOp (folded rank1 iota) + BroadCastInDimOp.
bool MatchConstIotaBroadCastInDim(DenseIntElementsAttr dimensions, Value iota) {
  if (dimensions.getNumElements() != 1) return false;
  auto iota_broadcast =
      dyn_cast_or_null<mhlo::BroadcastInDimOp>(iota.getDefiningOp());