[Bug target/105251] static assert sizeof(decltype(_together)) <= hardware_constructive_interference_size fails with gcc12

[raj.khem at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105251

--- Comment #9 from Khem Raj <raj.khem at gmail dot com> ---
how does something like this look ?

#include <cstdint>
#include <cstddef>
#include <new>
#include <algorithm>

#ifdef __cpp_lib_hardware_interference_size
    using std::hardware_constructive_interference_size;
    using std::hardware_destructive_interference_size;
#else
    // 64 bytes on x86-64 │ L1_CACHE_BYTES │ L1_CACHE_SHIFT │
__cacheline_aligned │ ...
    constexpr std::size_t hardware_constructive_interference_size = 64;
    constexpr std::size_t hardware_destructive_interference_size = 64;
#endif

class NetworkCounter {

private:
        template <typename T, size_t alignment>
        struct alignas(alignment) WithAlignment : T {
                using T::T;
        };

    template <typename T, size_t alignment>
    using WithAlignmentAtLeast = WithAlignment<T, std::max(alignof(T),
alignment)>;

    // These two counters are always incremented at the same time, so
    // we place them on the same cache line.
    template <typename T>
        using CacheAligned = WithAlignmentAtLeast<T,
hardware_constructive_interference_size>;
    struct Together {
        long long logicalBytesIn{0};
        long long requests{0};
    };
    CacheAligned<Together> _together{};
    static_assert(sizeof(decltype(_together)) <=
hardware_destructive_interference_size,
                  "cache line spill");
};