LogicalResult matchAndRewrite(
      mhlo::WhileOp while_op, OpAdaptor adaptor,
      ConversionPatternRewriter& rewriter) const final {
    // HLO WhileOp should have two regions: cond and body.
    if (while_op->getNumRegions() != 2) return failure();

    // This rule doesn't support mhlo::WhileOp with tuple inputs.
    for (auto type : while_op->getOperandTypes()) {
      if (mlir::isa<TupleType>(type)) return failure();
    }

    } else {
      mhlo_op = rewriter.create<DstOpT>(loc, op.getResultTypes(),
                                        adaptor.getOperands());
    }

    int64_t num_regions = op.getNumRegions();
    for (int64_t idx = 0; idx < num_regions; ++idx) {
      Region &region = mhlo_op.getBodyRegion(idx);
      rewriter.inlineRegionBefore(op.getBodyRegion(idx), region, region.end());