LLVM SmallVector

smallvec.cpp

#include "llvm/ADT/SmallVector.h"

#include <array>
#include <chrono>
#include <cstdint>
#include <iostream>
#include <vector>

struct Message { std::array<char, 128> data { }; };

template<bool fast> struct Packet { };
template<> struct Packet<false> { std::vector<Message> messages; };
template<> struct Packet<true> { llvm::SmallVector<Message, 3> messages; };

template<bool fast> void bench(size_t N) {
    using namespace std::chrono;

    std::cout << "Running, N = " << N << ", fast = " << fast << "... ";
    auto t0 = high_resolution_clock::now();
    Message m;
    for (size_t i = 0; i < N; i++) {
        Packet<fast> p;
        p.messages.push_back(m); p.messages.push_back(m); p.messages.push_back(m);
    }
    auto t1 = high_resolution_clock::now();
    auto d = duration_cast<microseconds>(t1 - t0).count();
    std::cout << "elapsed: " << d << " µs" << std::endl;
}

int main() {
    bench<false>(1000); bench<true>(1000);
    bench<false>(10000); bench<true>(10000);
    bench<false>(100000); bench<true>(100000);
}

Running, N = 1000, fast = 0... elapsed: 355 µs
Running, N = 1000, fast = 1... elapsed: 11 µs
Running, N = 10000, fast = 0... elapsed: 2886 µs
Running, N = 10000, fast = 1... elapsed: 139 µs
Running, N = 100000, fast = 0... elapsed: 37927 µs
Running, N = 100000, fast = 1... elapsed: 1329 µs