DataHandlerGPU: Core functionality (#21)

elsa/core/DataContainer.cpp

@@ -53,7 +53,7 @@ namespace elsa
                 _dataHandler = other._dataHandler->clone();
             }
 
-            _dataHandlerType = other._dataHandlerType;
+            // TODO: Check what to do with handler type if CPU copy assign to GPU type
         }
 
         return *this;
@@ -81,7 +81,7 @@ namespace elsa
             _dataHandler = std::move(other._dataHandler);
         }
 
-        _dataHandlerType = std::move(other._dataHandlerType);
+        // TODO: Check what to do with handler type if CPU move assign to GPU type
 
         // leave other in a valid state
         other._dataDescriptor = nullptr;
@@ -230,6 +230,12 @@ namespace elsa
                 return std::make_unique<DataHandlerCPU<data_t>>(std::forward<Args>(args)...);
             case DataHandlerType::MAP_CPU:
                 return std::make_unique<DataHandlerCPU<data_t>>(std::forward<Args>(args)...);
+#ifdef ELSA_CUDA_VECTOR
+            case DataHandlerType::GPU:
+                return std::make_unique<DataHandlerGPU<data_t>>(std::forward<Args>(args)...);
+            case DataHandlerType::MAP_GPU:
+                return std::make_unique<DataHandlerGPU<data_t>>(std::forward<Args>(args)...);
+#endif
             default:
                 throw std::invalid_argument("DataContainer: unknown handler type");
         }
@@ -277,8 +283,13 @@ namespace elsa
         const auto& ithDesc = blockDesc->getDescriptorOfBlock(i);
         index_t blockSize = ithDesc.getNumberOfCoefficients();
 
+        DataHandlerType newHandlerType = (_dataHandlerType == DataHandlerType::CPU
+                                          || _dataHandlerType == DataHandlerType::MAP_CPU)
+                                             ? DataHandlerType::MAP_CPU
+                                             : DataHandlerType::MAP_GPU;
+
         return DataContainer<data_t>{ithDesc, _dataHandler->getBlock(startIndex, blockSize),
-                                     DataHandlerType::MAP_CPU};
+                                     newHandlerType};
     }
 
     template <typename data_t>
@@ -295,10 +306,15 @@ namespace elsa
         const auto& ithDesc = blockDesc->getDescriptorOfBlock(i);
         index_t blockSize = ithDesc.getNumberOfCoefficients();
 
+        DataHandlerType newHandlerType = (_dataHandlerType == DataHandlerType::CPU
+                                          || _dataHandlerType == DataHandlerType::MAP_CPU)
+                                             ? DataHandlerType::MAP_CPU
+                                             : DataHandlerType::MAP_GPU;
+
         // getBlock() returns a pointer to non-const DH, but that's fine as it gets wrapped in a
         // constant container
         return DataContainer<data_t>{ithDesc, _dataHandler->getBlock(startIndex, blockSize),
-                                     DataHandlerType::MAP_CPU};
+                                     newHandlerType};
     }
 
     template <typename data_t>
@@ -307,8 +323,13 @@ namespace elsa
         if (dataDescriptor.getNumberOfCoefficients() != getSize())
             throw std::invalid_argument("DataContainer: view must have same size as container");
 
+        DataHandlerType newHandlerType = (_dataHandlerType == DataHandlerType::CPU
+                                          || _dataHandlerType == DataHandlerType::MAP_CPU)
+                                             ? DataHandlerType::MAP_CPU
+                                             : DataHandlerType::MAP_GPU;
+
         return DataContainer<data_t>{dataDescriptor, _dataHandler->getBlock(0, getSize()),
-                                     DataHandlerType::MAP_CPU};
+                                     newHandlerType};
     }
 
     template <typename data_t>
@@ -318,10 +339,15 @@ namespace elsa
         if (dataDescriptor.getNumberOfCoefficients() != getSize())
             throw std::invalid_argument("DataContainer: view must have same size as container");
 
+        DataHandlerType newHandlerType = (_dataHandlerType == DataHandlerType::CPU
+                                          || _dataHandlerType == DataHandlerType::MAP_CPU)
+                                             ? DataHandlerType::MAP_CPU
+                                             : DataHandlerType::MAP_GPU;
+
         // getBlock() returns a pointer to non-const DH, but that's fine as it gets wrapped in a
         // constant container
         return DataContainer<data_t>{dataDescriptor, _dataHandler->getBlock(0, getSize()),
-                                     DataHandlerType::MAP_CPU};
+                                     newHandlerType};
     }
 
     template <typename data_t>
@@ -396,22 +422,6 @@ namespace elsa
         return const_reverse_iterator(cbegin());
     }
 
-    template <typename data_t>
-    typename DataContainer<data_t>::HandlerTypes_t DataContainer<data_t>::getHandlerPtr() const
-    {
-        DataContainer<data_t>::HandlerTypes_t handler;
-
-        if (_dataHandlerType == DataHandlerType::CPU) {
-            handler = static_cast<DataHandlerCPU<data_t>*>(_dataHandler.get());
-        }
-
-        if (_dataHandlerType == DataHandlerType::MAP_CPU) {
-            handler = static_cast<DataHandlerMapCPU<data_t>*>(_dataHandler.get());
-        }
-
-        return handler;
-    }
-
     template <typename data_t>
     DataHandlerType DataContainer<data_t>::getDataHandlerType() const
     {

elsa/core/DataHandler.h

@@ -4,6 +4,10 @@
 #include "Cloneable.h"
 #include "ExpressionPredicates.h"
 
+#ifdef ELSA_CUDA_VECTOR
+#include "Quickvec.h"
+#endif
+
 #include <Eigen/Core>
 
 namespace elsa
@@ -29,13 +33,6 @@ namespace elsa
     template <typename data_t = real_t>
     class DataHandler : public Cloneable<DataHandler<data_t>>
     {
-        /// for enabling accessData()
-        template <class Operand, std::enable_if_t<isDataContainer<Operand>, int>>
-        friend constexpr auto evaluateOrReturn(Operand const& operand);
-
-        /// for enabling accessData()
-        friend DataContainer<data_t>;
-
     protected:
         /// convenience typedef for the Eigen::Matrix data vector
         using DataVector_t = Eigen::Matrix<data_t, Eigen::Dynamic, 1>;
@@ -178,11 +175,5 @@ namespace elsa
 
         /// derived classes should override this method to implement move assignment
         virtual void assign(DataHandler<data_t>&& other) = 0;
-
-        /// derived classes return underlying data
-        virtual DataMap_t accessData() = 0;
-
-        /// derived classes return underlying data
-        virtual DataMap_t accessData() const = 0;
     };
 } // namespace elsa

elsa/core/DataHandlerCPU.h

@@ -18,7 +18,7 @@ namespace elsa
     class DataHandlerCPU;
     // forward declaration, used for testing and defined in test file (declared as friend)
     template <typename data_t>
-    long useCount(const DataHandlerCPU<data_t>&);
+    long useCount(const DataHandlerCPU<data_t>& /*dh*/);
 
     /**
      * \brief Class representing and owning a vector stored in CPU main memory (using
@@ -45,9 +45,16 @@ namespace elsa
         /// declare DataHandlerMapCPU as friend, allows the use of Eigen for improved performance
         friend DataHandlerMapCPU<data_t>;
 
+        /// for enabling accessData()
+        friend DataContainer<data_t>;
+
         /// used for testing only and defined in test file
         friend long useCount<>(const DataHandlerCPU<data_t>& dh);
 
+        /// friend constexpr function to implement expression templates
+        template <bool GPU, class Operand, std::enable_if_t<isDataContainer<Operand>, int>>
+        friend constexpr auto evaluateOrReturn(Operand const& operand);
+
     protected:
         /// convenience typedef for the Eigen::Matrix data vector
         using DataVector_t = Eigen::Matrix<data_t, Eigen::Dynamic, 1>;
@@ -176,10 +183,10 @@ namespace elsa
         void assign(DataHandler<data_t>&& other) override;
 
         /// return non-const version of data
-        DataMap_t accessData() override;
+        DataMap_t accessData();
 
         /// return const version of data
-        DataMap_t accessData() const override;
+        DataMap_t accessData() const;
 
     private:
         /// creates the deep copy for the copy-on-write mechanism

elsa/core/DataHandlerGPU.h

+#pragma once
+
+#include "elsaDefines.h"
+#include "DataHandler.h"
+#include "Quickvec.h"
+
+#include <list>
+
+namespace elsa
+{
+    // forward declaration, allows mutual friending
+    template <typename data_t>
+    class DataHandlerMapGPU;
+
+    // forward declaration for friend test function
+    template <typename data_t = real_t>
+    class DataHandlerGPU;
+    // forward declaration, used for testing and defined in test file (declared as friend)
+    template <typename data_t>
+    long useCount(const DataHandlerGPU<data_t>&);
+
+    /**
+     * \brief Class representing and owning a vector stored in CPU main memory (using
+     * Eigen::Matrix).
+     *
+     * \tparam data_t - data type that is stored, defaulting to real_t.
+     *
+     * \author David Frank - main code
+     * \author Tobias Lasser - modularization and modernization
+     * \author Nikola Dinev - integration of map and copy-on-write concepts
+     *
+     * The class implements copy-on-write. Therefore any non-const functions should call the
+     * detach() function first to trigger the copy-on-write mechanism.
+     *
+     * DataHandlerGPU and DataHandlerMapCPU are mutual friend classes allowing for the vectorization
+     * of arithmetic operations with the help of Eigen. A strong bidirectional link exists
+     * between the two classes. A Map is associated with the DataHandlerGPU from which it was
+     * created for the entirety of its lifetime. If the DataHandlerGPU starts managing a new vector
+     * (e.g. through a call to detach()), all associated Maps will also be updated.
+     */
+    template <typename data_t>
+    class DataHandlerGPU : public DataHandler<data_t>
+    {
+        /// for enabling accessData()
+        friend DataContainer<data_t>;
+
+        /// declare DataHandlerMapGPU as friend, allows the use of Eigen for improved performance
+        friend DataHandlerMapGPU<data_t>;
+
+        /// used for testing only and defined in test file
+        friend long useCount<>(const DataHandlerGPU<data_t>& dh);
+
+        /// friend constexpr function to implement expression templates
+        template <bool GPU, class Operand, std::enable_if_t<isDataContainer<Operand>, int>>
+        friend constexpr auto evaluateOrReturn(Operand const& operand);
+
+    protected:
+        /// convenience typedef for the Eigen::Matrix data vector
+        using DataVector_t = Eigen::Matrix<data_t, Eigen::Dynamic, 1>;
+
+        /// convenience typedef for the Eigen::Map
+        using DataMap_t = Eigen::Map<DataVector_t>;
+
+    public:
+        /// delete default constructor (having no information makes no sense)
+        DataHandlerGPU() = delete;
+
+        /// default destructor
+        ~DataHandlerGPU() override;
+
+        /**
+         * \brief Constructor initializing an appropriately sized vector with zeros
+         *
+         * \param[in] size of the vector
+         * \param[in] initialize - set to false if you do not need initialization with zeros
+         * (default: true)
+         *
+         * \throw std::invalid_argument if the size is non-positive
+         */
+        explicit DataHandlerGPU(index_t size);
+
+        /**
+         * \brief Constructor initializing a data vector with a given vector
+         *
+         * \param[in] vector that is used for initializing the data
+         */
+        explicit DataHandlerGPU(DataVector_t const& vector);
+
+        /**
+         * \brief Constructor initializing a data vector with a given vector
+         *
+         * \param[in] vector that is used for initializing the data
+         */
+        explicit DataHandlerGPU(quickvec::Vector<data_t> const& vector);
+        /// copy constructor
+        DataHandlerGPU(const DataHandlerGPU<data_t>& other);
+
+        /// move constructor
+        DataHandlerGPU(DataHandlerGPU<data_t>&& other) noexcept;
+
+        /// return the size of the vector
+        index_t getSize() const override;
+
+        /// return the index-th element of the data vector (not bounds checked!)
+        data_t& operator[](index_t index) override;
+
+        /// return the index-th element of the data vector as read-only (not bound checked!)
+        const data_t& operator[](index_t index) const override;
+
+        /// return the dot product of the data vector with vector v
+        data_t dot(const DataHandler<data_t>& v) const override;
+
+        /// return the squared l2 norm of the data vector (dot product with itself)
+        GetFloatingPointType_t<data_t> squaredL2Norm() const override;
+
+        /// return the l1 norm of the data vector (sum of absolute values)
+        GetFloatingPointType_t<data_t> l1Norm() const override;
+
+        /// return the linf norm of the data vector (maximum of absolute values)
+        GetFloatingPointType_t<data_t> lInfNorm() const override;
+
+        /// return the sum of all elements of the data vector
+        data_t sum() const override;
+
+        /// copy assign another DataHandlerGPU
+        DataHandlerGPU<data_t>& operator=(const DataHandlerGPU<data_t>& v);
+
+        /// move assign another DataHandlerGPU
+        DataHandlerGPU<data_t>& operator=(DataHandlerGPU<data_t>&& v);
+
+        /// lift copy and move assignment operators from base class
+        using DataHandler<data_t>::operator=;
+
+        /// compute in-place element-wise addition of another vector v
+        DataHandler<data_t>& operator+=(const DataHandler<data_t>& v) override;
+
+        /// compute in-place element-wise subtraction of another vector v
+        DataHandler<data_t>& operator-=(const DataHandler<data_t>& v) override;
+
+        /// compute in-place element-wise multiplication by another vector v
+        DataHandler<data_t>& operator*=(const DataHandler<data_t>& v) override;
+
+        /// compute in-place element-wise division by another vector v
+        DataHandler<data_t>& operator/=(const DataHandler<data_t>& v) override;
+
+        /// compute in-place addition of a scalar
+        DataHandler<data_t>& operator+=(data_t scalar) override;
+
+        /// compute in-place subtraction of a scalar
+        DataHandler<data_t>& operator-=(data_t scalar) override;
+
+        /// compute in-place multiplication by a scalar
+        DataHandler<data_t>& operator*=(data_t scalar) override;
+
+        /// compute in-place division by a scalar
+        DataHandler<data_t>& operator/=(data_t scalar) override;
+
+        /// assign a scalar to all elements of the data vector
+        DataHandler<data_t>& operator=(data_t scalar) override;
+
+        /// return a reference to the sequential block starting at startIndex and containing
+        /// numberOfElements elements
+        std::unique_ptr<DataHandler<data_t>> getBlock(index_t startIndex,
+                                                      index_t numberOfElements) override;
+        /// return a const reference to the sequential block starting at startIndex and containing
+        /// numberOfElements elements
+        std::unique_ptr<const DataHandler<data_t>>
+            getBlock(index_t startIndex, index_t numberOfElements) const override;
+
+    protected:
+        /// the vector storing the data
+        std::shared_ptr<quickvec::Vector<data_t>> _data;
+
+        /// list of DataHandlerMaps referring to blocks of this
+        std::list<DataHandlerMapGPU<data_t>*> _associatedMaps;
+
+        /// implement the polymorphic clone operation
+        DataHandlerGPU<data_t>* cloneImpl() const override;
+
+        /// implement the polymorphic comparison operation
+        bool isEqual(const DataHandler<data_t>& other) const override;
+
+        /// copy the data stored in other
+        void assign(const DataHandler<data_t>& other) override;
+
+        /// move the data stored in other if other is of the same type, otherwise copy the data
+        void assign(DataHandler<data_t>&& other) override;
+
+        /// return non-const version of data
+        quickvec::Vector<data_t> accessData();
+
+        /// return const version of data
+        quickvec::Vector<data_t> accessData() const;
+
+    private:
+        /// creates the deep copy for the copy-on-write mechanism
+        void detach();
+
+        /// same as detach() but leaving an uninitialized block of numberOfElements elements
+        /// starting at index startIndex
+        void detachWithUninitializedBlock(index_t startIndex, index_t numberOfElements);
+
+        /// change the vector being handled
+        void attach(const std::shared_ptr<quickvec::Vector<data_t>>& data);
+
+        /// change the vector being handled (rvalue version)
+        void attach(std::shared_ptr<quickvec::Vector<data_t>>&& data);
+    };
+} // namespace elsa

elsa/core/DataHandlerMapCPU.h

@@ -45,6 +45,13 @@ namespace elsa
         /// declare DataHandlerCPU as friend, allows the use of Eigen for improved performance
         friend class DataHandlerCPU<data_t>;
 
+        /// friend constexpr function to implement expression templates
+        template <bool GPU, class Operand, std::enable_if_t<isDataContainer<Operand>, int>>
+        friend constexpr auto evaluateOrReturn(Operand const& operand);
+
+        /// for enabling accessData()
+        friend DataContainer<data_t>;
+
     protected:
         /// convenience typedef for the Eigen::Matrix data vector
         using DataVector_t = Eigen::Matrix<data_t, Eigen::Dynamic, 1>;
@@ -152,10 +159,10 @@ namespace elsa
         void assign(DataHandler<data_t>&& other) override;
 
         /// return non-const version of the data
-        DataMap_t accessData() override;
+        DataMap_t accessData();
 
         /// return const version of the data
-        DataMap_t accessData() const override;
+        DataMap_t accessData() const;
 
     private:
         /**

elsa/core/DataHandlerMapGPU.h

+#pragma once
+
+#include "elsaDefines.h"
+#include "DataHandler.h"
+#include "Quickvec.h"
+
+#include <Eigen/Core>
+
+#include <list>
+
+namespace elsa
+{
+    /// forward declaration, allows mutual friending
+    template <typename data_t>
+    class DataHandlerGPU;
+
+    /**
+     * \brief Class referencing a vector stored in GPU main memory, or a part thereof
+     *
+     * \tparam data_t data type of vector
+     *
+     * \author David Frank - main code
+     * \author Tobias Lasser - modularization, fixes
+     * \author Nikola Dinev - integration with the copy-on-write mechanism
+     * \author Jens Petit - adaption of CPU version for GPU
+     *
+     * This class does not own or manage its own memory. It is bound to a DataHandlerGPU (the data
+     * owner) at its creation, and serves as a reference to a sequential block of memory owned by
+     * the DataHandlerGPU. As such, changes to the Map will affect the DataHandlerGPU and vice
+     * versa.
+     *
+     * Maps do not support move assignment, and remain bound to the original data owner until
+     * destructed.
+     *
+     * Maps provide only limited support for copy-on-write. Unless the Map is referencing the
+     * entirety of the vector managed by the data owner, assigning to the Map or cloning will always
+     * trigger a deep copy.
+     *
+     * Cloning a Map produces a new DataHandlerGPU, managing a new chunk of memory. The contents of
+     * the memory are equivalent to the contents of the block referenced by the Map, but the two are
+     * not associated.
+     */
+    template <typename data_t = real_t>
+    class DataHandlerMapGPU : public DataHandler<data_t>
+    {
+        /// declare DataHandlerGPU as friend, allows the use of Eigen for improved performance
+        friend class DataHandlerGPU<data_t>;
+
+        /// friend constexpr function to implement expression templates
+        template <bool GPU, class Operand, std::enable_if_t<isDataContainer<Operand>, int>>
+        friend constexpr auto evaluateOrReturn(Operand const& operand);
+
+        /// for enabling accessData()
+        friend DataContainer<data_t>;
+
+    public:
+        /// copy constructor
+        DataHandlerMapGPU(const DataHandlerMapGPU<data_t>& other);
+
+        /// default move constructor
+        DataHandlerMapGPU(DataHandlerMapGPU<data_t>&& other) = default;
+
+        /// default destructor
+        ~DataHandlerMapGPU() override;
+
+        /// return the size of the vector
+        index_t getSize() const override;
+
+        /// return the index-th element of the data vector (not bounds checked!)
+        data_t& operator[](index_t index) override;
+
+        /// return the index-th element of the data vector as read-only (not bound checked!)
+        const data_t& operator[](index_t index) const override;
+
+        /// return the dot product of the data vector with vector v
+        data_t dot(const DataHandler<data_t>& v) const override;
+
+        /// return the squared l2 norm of the data vector (dot product with itself)
+        GetFloatingPointType_t<data_t> squaredL2Norm() const override;
+
+        /// return the l1 norm of the data vector (sum of absolute values)
+        GetFloatingPointType_t<data_t> l1Norm() const override;
+
+        /// return the linf norm of the data vector (maximum of absolute values)
+        GetFloatingPointType_t<data_t> lInfNorm() const override;
+
+        /// return the sum of all elements of the data vector
+        data_t sum() const override;
+
+        /// compute in-place element-wise addition of another vector v
+        DataHandler<data_t>& operator+=(const DataHandler<data_t>& v) override;
+
+        /// compute in-place element-wise subtraction of another vector v
+        DataHandler<data_t>& operator-=(const DataHandler<data_t>& v) override;
+
+        /// compute in-place element-wise multiplication by another vector v
+        DataHandler<data_t>& operator*=(const DataHandler<data_t>& v) override;
+
+        /// compute in-place element-wise division by another vector v
+        DataHandler<data_t>& operator/=(const DataHandler<data_t>& v) override;
+
+        /// copy assign another DataHandlerMapGPU to this, other types handled in assign()
+        DataHandlerMapGPU<data_t>& operator=(const DataHandlerMapGPU<data_t>& v);
+
+        DataHandlerMapGPU<data_t>& operator=(DataHandlerMapGPU<data_t>&&) = default;
+
+        /// lift copy and move assignment operators from base class
+        using DataHandler<data_t>::operator=;
+
+        /// compute in-place addition of a scalar
+        DataHandler<data_t>& operator+=(data_t scalar) override;
+
+        /// compute in-place subtraction of a scalar
+        DataHandler<data_t>& operator-=(data_t scalar) override;
+
+        /// compute in-place multiplication by a scalar
+        DataHandler<data_t>& operator*=(data_t scalar) override;
+
+        /// compute in-place division by a scalar
+        DataHandler<data_t>& operator/=(data_t scalar) override;
+
+        /// assign a scalar to all elements of the data vector
+        DataHandler<data_t>& operator=(data_t scalar) override;
+
+        /// return a reference to the sequential block starting at startIndex and containing
+        /// numberOfElements elements
+        std::unique_ptr<DataHandler<data_t>> getBlock(index_t startIndex,
+                                                      index_t numberOfElements) override;
+
+        /// return a const reference to the sequential block starting at startIndex and containing
+        /// numberOfElements elements
+        std::unique_ptr<const DataHandler<data_t>>
+            getBlock(index_t startIndex, index_t numberOfElements) const override;
+
+    protected:
+        /// vector mapping of the data
+        quickvec::Vector<data_t> _map;
+
+        /// pointer to the data-owning handler
+        DataHandlerGPU<data_t>* _dataOwner;
+
+        /// handle to this in the list of Maps associated with the data-owning handler
+        typename std::list<DataHandlerMapGPU<data_t>*>::iterator _handle;
+
+        /// implement the polymorphic clone operation
+        DataHandlerGPU<data_t>* cloneImpl() const override;
+
+        /// implement the polymorphic comparison operation
+        bool isEqual(const DataHandler<data_t>& other) const override;
+
+        void assign(const DataHandler<data_t>& other) override;
+
+        void assign(DataHandler<data_t>&& other) override;
+
+        /// return non-const version of the data
+        quickvec::Vector<data_t> accessData();
+
+        /// return const version of the data
+        quickvec::Vector<data_t> accessData() const;
+
+    private:
+        /**
+         * \brief Construct a DataHandlerMapGPU referencing a sequential block of data owned by
+         * DataHandlerGPU
+         *
+         * \param[in] dataOwner pointer to the DataHandlerGPU owning the data vector
+         * \param[in] data pointer to start of segment
+         * \param[in] n number of elements in block
+         */
+        DataHandlerMapGPU(DataHandlerGPU<data_t>* dataOwner, data_t* data, index_t n);
+    };
+} // namespace elsa

elsa/core/Expression.h

@@ -6,28 +6,56 @@
 #include <optional>
 #include "DataDescriptor.h"
 #include "ExpressionPredicates.h"
+#include "DataHandlerCPU.h"
+#include "DataHandlerMapCPU.h"
+
+#ifdef ELSA_CUDA_VECTOR
+#include "DataHandlerGPU.h"
+#endif
 
 namespace elsa
 {
     /// Compile time switch to select to recursively evaluate for expression type
-    template <class Operand, std::enable_if_t<isExpression<Operand>, int> = 0>
+    template <bool GPU, class Operand, std::enable_if_t<isExpression<Operand>, int> = 0>
     constexpr auto evaluateOrReturn(Operand const& operand)
     {
-        return operand.eval();
+        return operand.template eval<GPU>();
     }
 
     /// Compile time switch to return-by-value of arithmetic types
-    template <class Operand, std::enable_if_t<isArithmetic<Operand>, int> = 0>
+    template <bool GPU, class Operand, std::enable_if_t<isArithmetic<Operand>, int> = 0>
     constexpr auto evaluateOrReturn(Operand const operand)
     {
         return operand;
     }
 
     /// Compile time switch to return data in container
-    template <class Operand, std::enable_if_t<isDataContainer<Operand>, int> = 0>
+    template <bool GPU, class Operand, std::enable_if_t<isDataContainer<Operand>, int> = 0>
     constexpr auto evaluateOrReturn(Operand const& operand)
     {
-        return operand._dataHandler->accessData();
+        using data_t = typename Operand::value_type;
+
+        if constexpr (GPU) {