Add a Stack operator

Context

The Stack operator is designed to be the counterpart of the Pop operator, which dictates its functionalities: at each time step t, it takes a tensor as input and stacks it along axis 0. The Pop operator overrides the getNbRequiredData() method, which specifies the amount of data consumed each time the operator is executed. Similarly, the Stack operator overrides the getNbRequiredMemory() method, which specifies the amount of data produced by the operator with each execution.

A notable difference from the Pop operator is the way we define the output tensor's dimensions (which has to be done statically). For Pop, this is straightforward: we simply take the input tensor's dimensions and remove the first dimension. For Stack, however, we define an attribute representing the maximum number of elements to stack. Then, given the input tensor shape, the output tensor will have an additional first dimension corresponding to the maximum number of elements to stack.

Of course, care must be taken during the scheduling phase and execution to ensure that the operator is not invoked more times than the defined maximum.

Modified files

• Stack.hpp and Stack.cpp : Cpp implementation;
• Test_StackImpl.cpp : Cpp unit tests;
• pybind_core.cpp and pybind_Stack.cpp : Added python bindings;

Detailed major modifications

TODO

• C++ Implementation
• Tests
• Python bindings

Scheduling tests are needed, but will be done in aidge_backend_cpu, as to have more flexibility (in particular, it would be interesting to test something like Pop->Dummy MetaOp->Stack and see how it goes).

include/aidge/operator/Stack.hpp

+#ifndef AIDGE_CORE_OPERATOR_STACK_H_
+#define AIDGE_CORE_OPERATOR_STACK_H_
+
+#include <memory>
+#include <string>
+
+#include "aidge/backend/OperatorImpl.hpp"
+#include "aidge/graph/Node.hpp"
+#include "aidge/operator/OperatorTensor.hpp"
+#include "aidge/utils/Registrar.hpp"
+#include "aidge/utils/StaticAttributes.hpp"
+#include "aidge/utils/Types.h"
+
+namespace Aidge {
+
+class StackOpImpl : public OperatorImpl {
+  public:
+    StackOpImpl(const Operator &op, const std::string &backend = "")
+        : OperatorImpl(op, backend) {}
+    void forward() override;
+};
+
+enum class StackAttr { MaxElements };
+
+class StackOp
+    : public OperatorTensor,
+      public Registrable<
+          StackOp,
+          std::string,
+          std::function<std::unique_ptr<OperatorImpl>(const StackOp &)>> {
+
+  private:
+    using Attributes_ = StaticAttributes<StackAttr, std::uint32_t>;
+    template <StackAttr e> using attr = typename Attributes_::template attr<e>;
+    const std::shared_ptr<Attributes_> mAttributes;
+
+  public:
+    static const std::string s_type;
+
+    StackOp(std::uint32_t maxElements);
+
+    /**
+     * @brief Copy-constructor. Copy the operator attributes and its output
+     * tensor(s), but not its input tensors (the new operator has no input
+     * associated).
+     * @param op Operator to copy.
+     */
+    StackOp(const StackOp &op);
+
+    /**
+     * @brief Clone the operator using its copy-constructor.
+     * @see Operator::StackOp
+     */
+    std::shared_ptr<Operator> clone() const override;
+
+    void setBackend(const std::string &name,
+                    DeviceIdx_t device = 0) override final;
+
+    std::set<std::string> getAvailableBackends() const override;
+
+    bool forwardDims(bool allowDataDependency = false) override final;
+    void forward() override;
+
+    inline std::shared_ptr<Attributes> attributes() const override {
+        return mAttributes;
+    }
+    inline std::uint32_t &maxElements() const {
+        return mAttributes->template getAttr<StackAttr::MaxElements>();
+    }
+
+    static const std::vector<std::string> getInputsName() {
+        return {"data_input"};
+    }
+    static const std::vector<std::string> getOutputsName() {
+        return {"data_output"};
+    }
+};
+
+std::shared_ptr<Node> stack(std::uint32_t maxElements,
+                            const std::string &name = "");
+} // namespace Aidge
+
+namespace {
+template <>
+const char *const EnumStrings<Aidge::StackAttr>::data[] = {"max_elements"};
+}
+
+#endif