视觉C++ 2017 错误?编译器优化表达式

以下一段代码给我带来了一些问题，特别是diff的评估：

#include <iostream>
template<typename T>
class array2d
{
protected:
    T* arr;
    int w, h;
public:
array2d() : arr(nullptr), w(0), h(0) {}
bool init(int w, int h)
{
    free();
    arr = new (std::nothrow) T[w*h];
    if (arr == nullptr)
    {
        std::cerr << "array2d::init(): Failed to allocate: " << w * h * sizeof(T) << " bytes.n";
        return false;
    }
    this->w = w;
    this->h = h;
    return true;
}
void fill(T v)
{
    for (int i = 0; i < w*h; ++i)
        arr[i] = v;
}
void free()
{
    if (arr != nullptr)
    {
        delete[] arr;
        arr = nullptr;
        w = 0;
        h = 0;
    }
}
template<typename U>
bool copy(const array2d<U>& v)
{
    if (!v)
    {
        std::cerr << "array2d::copy(): Input array is empty.n";
        return false;
    }
    if (w*h != v.width()*v.height())
    {
        if (!init(v.width(), v.height())) return false;
    }
    for (int i = 0; i < w*h; ++i)
        arr[i] = static_cast<T>(v(i));
    return true;
}
inline T operator()(int i) const { return arr[i]; }
inline T& operator()(int i) { return arr[i]; }
inline T operator[](int i) const { return arr[i]; }
inline T& operator[](int i) { return arr[i]; }
inline T operator()(int x, int y) const { return arr[x + y*w]; }
inline T& operator()(int x, int y) { return arr[x + y*w]; }
inline int width() const { return w; }
inline int height() const { return h; }
inline const T* get() const { return arr; }
inline T* get() { return arr; }
operator bool() const { return arr != nullptr; }
array2d<T>& operator*=(T v)
{
    for (int i = 0; i < w*h; ++i)
        arr[i] *= v;
    return *this;
}
~array2d() { free(); }
};
typedef unsigned long long uint64;
uint64 computeErrors(const array2d<uint64>& a, const array2d<uint64>& b)
{
    uint64 MNE = 0;
    for (int i = 0; i < a.height()*a.width(); ++i)
    {
        uint64 diff = ((a[i] >= b[i]) ? a[i] - b[i] : b[i] - a[i]);
        if (a[i] != b[i])
        {
            std::cout << "Diff: " << diff << "n";
            std::cout << "What diff should equal to: " << ((a[i] >= b[i]) ? a[i] - b[i] : b[i] - a[i]) << "n";
        }
        if (i == 0)
        {
            std::cout << "Diff should not be 0, but it is: " << diff << "n";
        }
        if (MNE < diff)
        {
            MNE = diff;
            std::cout << "We should reach this, but we don't.n";
        }
    }
    return MNE;
}

int main()
{
    int w = 1;
    int h = 1;
    array2d<uint64> a;
    if (!a.init(w,h)) return 1;
    a.fill(0);
    array2d<uint64> b;
    if (!b.init(w,h)) return 1;
    b.fill(0);
    a[0] = 0ull;
    b[0] = 1;
    std::cout << a[0] << " " << b[0] << "n";
    auto e = computeErrors(a, b);
    std::cout << "MNE: " << e << "n";
    return 0;
}

如果我用/O1、/O2 或/Ox;用/Ot 和/Ob2 编译它，那么 diff 总是 0，而它不应该是。如果我在没有/Ot 或没有/Ob2 的情况下编译，一切都按预期工作。此代码中是否有任何格式不正确的内容？我在这里附上了整个事情：http://coliru.stacked-crooked.com/a/245f23f05df39418。但是，如果我更改数组的 [] 运算符以返回 const T&而不是 T，则一切正常。这是编译器错误吗？还是我在运算符中返回 T 而不是 const T&不好(我返回 T，因为我在某处读到按值传递较小的 POD 更快，就我而言，我有一些带有 uint32 的数组，其中速度非常重要(。我目前正在使用 Visual C++ 2017。

编辑：根据user4581301的建议，我也在这里添加了整个代码。

编辑2：这是我_MSC_FULL_VER：191125547。