if (lhs_index == lhs_map.end()) {
      // out only isn't supported
      return std::nullopt;
    }
  }
  return dnums;
}

std::optional<EinsumDimensionNumbers> GetEinsumDimensionNumbers(
    llvm::StringRef equation, RankedTensorType lhs_ty,
    RankedTensorType rhs_ty) {
  llvm::StringRef lhs_rhs;
  llvm::StringRef out;
  std::tie(lhs_rhs, out) = equation.split("->");