vtr_memory.h

#ifndef VTR_MEMORY_H
#define VTR_MEMORY_H
#include <cstddef>
#include <cstdlib>
#include <new>

#ifdef _WIN32
#    include <cerrno>
#    include <malloc.h>
#endif

namespace vtr {

/**
 * @brief This function will force the container to be cleared
 *
 * It release its held memory.
 * For efficiency, STL containers usually don't
 * release their actual heap-allocated memory until
 * destruction (even if Container::clear() is called).
 */
template<typename Container>
void release_memory(Container& container) {
    ///@brief Force a re-allocation to happen by swapping in a new (empty) container.
    Container().swap(container);
}

struct t_linked_vptr; //Forward declaration

/**
 * This structure keeps track to chenks of memory
 *
 * This structure is to keep track of chunks of memory that is being	
 * allocated to save overhead when allocating very small memory pieces. 
 * For a complete description, please see the comment in chunk_malloc
 */
struct t_chunk {
    t_linked_vptr* chunk_ptr_head = nullptr;

    //chunk_ptr_head->data_vptr: head of the entire linked
    //list of allocated "chunk" memory;
    //chunk_ptr_head->next: pointer to the next chunk on the linked list
    int mem_avail = 0;                ///< number of bytes left in the current chunk
    char* next_mem_loc_ptr = nullptr; ///< pointer to the first available (free) byte in the current chunk
};

void* free(void* some);
void* calloc(size_t nelem, size_t size);
void* malloc(size_t size);
void* realloc(void* ptr, size_t size);

void* chunk_malloc(size_t size, t_chunk* chunk_info);
void free_chunk_memory(t_chunk* chunk_info);

///@brief Like chunk_malloc, but with proper C++ object initialization
template<typename T>
T* chunk_new(t_chunk* chunk_info) {
    void* block = chunk_malloc(sizeof(T), chunk_info);

    return new (block) T(); //Placement new
}

///@brief Call the destructor of an obj which must have been allocated in the specified chunk
template<typename T>
void chunk_delete(T* obj, t_chunk* /*chunk_info*/) {
    if (obj) {
        obj->~T(); // Manually call destructor
        // Currently we don't mark the unused memory as free
    }
}

/**
 * @brief Cross platform wrapper around GNU's malloc_trim()
 *
 * TODO: This is only used in one place within VPR, consider removing it
 */
int malloc_trim(size_t pad);

inline int memalign(void** ptr_out, size_t align, size_t size) {
#ifdef _WIN32
    void* temp_ptr = _aligned_malloc(size, align);
    if (temp_ptr != NULL) {
        *ptr_out = temp_ptr;
        return 0;
    } else {
        return errno;
    }
#else
    return posix_memalign(ptr_out, align, size);
#endif
}

/**
 * @brief A macro generates a prefetch instruction on all architectures that include it.
 * 
 * This is all modern x86 and ARM64 platforms.
 *
 * This is a macro because it has to be.  rw and locality must be constants,
 * not just constexpr.
 */
#define VTR_PREFETCH(addr, rw, locality) __builtin_prefetch(addr, rw, locality)

/**
 * @brief aligned_allocator is a STL allocator that allocates memory in an aligned fashion
 *
 * works if supported by the platform
 * 
 * It is worth noting the C++20 std::allocator does aligned allocations, but
 * C++20 has poor support.
 */
template<class T>
struct aligned_allocator {
    using value_type = T;
    using pointer = T*;
    using const_pointer = const T*;
    using reference = T&;
    using const_reference = const T&;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;

    pointer allocate(size_type n, const void* /*hint*/ = 0) {
        void* data;
        int ret = vtr::memalign(&data, alignof(T), sizeof(T) * n);
        if (ret != 0) {
            throw std::bad_alloc();
        }
        return static_cast<pointer>(data);
    }

    void deallocate(T* p, size_type /*n*/) {
#ifdef _WIN32
        _aligned_free(p);
#else
        vtr::free(p);
#endif
    }
};

/**
 * @brief compare two aligned_allocators.
 *
 * Since the allocator doesn't have any internal state, all allocators for a given type are the same.
 */
template<typename T>
bool operator==(const aligned_allocator<T>&, const aligned_allocator<T>&) {
    return true;
}

} // namespace vtr

#endif