// Pad 0s in front of the begin.
  TF::ConstOp new_begin =
      PadConstValues(begin.getDefiningOp(), 0, 4, slice_op.getLoc(), &rewriter);
  if (!new_begin) return failure();

  // Pad 1s in front of the size.
  TF::ConstOp new_size =
      PadConstValues(size.getDefiningOp(), 1, 4, slice_op.getLoc(), &rewriter);
  if (!new_size) return failure();

  // Reshape the input to 4d.