addArgumentMaterialization(MaterializeIllegalCast);
    addSourceMaterialization(MaterializeIllegalCast);
    addTargetMaterialization(MaterializeIllegalCast);
  }

  Attribute convertEncoding(Attribute attr) const final {
    LLVM_DEBUG(llvm::dbgs() << "Converting encoding.\n" << attr << '\n');
    // Must be VHLO encoding, or convertible to VHLO encoding.
    if (attr.getDialect().getNamespace() ==

    });
    addConversion([](mlir::stablehlo::TokenType token) -> mlir::Type {
      return mlir::vhlo::TokenV1Type::get(token.getContext());
    });
    addBuiltinToVhloConversions();
  }

  mlir::Attribute convertEncoding(mlir::Attribute attr) const final {
    // Must be VHLO encoding, or convertible to VHLO encoding.
    if (attr.getDialect().getNamespace() ==
        mlir::vhlo::VhloDialect::getDialectNamespace())
      return attr;