测试结果：
gcc7/gcc9：
    优化：g++ foo.cc -o foo -O2 -fopenmp
    malloc: 0ms
    new: 900ms
vs2017：
    优化：默认Release
    new/malloc: 200ms

看上去vs的运行结果比较正常，怎么解释这个？

测试代码如下：
#include <chrono>
#include <iostream>
#include <string.h>

using namespace std::chrono;

void test_copy() {
    const long N = 1 * 1024 * 1024 * 1024L;
    char *src = (char *)malloc(N);
    if (!src) {
        printf("src null\n");
        return;
    }
    char *dst = (char *)malloc(N);
    if (!dst) {
        printf("dst null\n");
        return;
    }
    // char *src = new char[N];
    // char *dst = new char[N];

    {
        auto begin = steady_clock::now();
#pragma omp parallel for
        for (long i = 0; i < N; i++) {
            src[i] = i;
        }
        auto end = steady_clock::now();
        auto duration = duration_cast<milliseconds>(end - begin);
        std::cout << "assign duration time: " << duration.count() << "ms\n";
    }

    auto begin = steady_clock::now();
    memcpy(dst, src, N);
    auto end = steady_clock::now();
    auto duration = duration_cast<milliseconds>(end - begin);
    std::cout << "memcpy duration time: " << duration.count() << "ms\n";

    // delete [] src;
    // delete [] dst;
    free(src);
    free(dst);
}

int main(int argc, char* argv[])
{
    test_copy();

    return 0;
}
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