gcc Compiler Segmentation Fault When Assigning from Value Captured Variable to Lambda Parameter

Question

I was working on this answer and wrote the code:

bool generate(vector<int>& temp, int& target, const size_t width, const size_t i) {
    const auto replacement = temp[i];
    const auto result = target > replacement;

    if (result) {
        for_each(begin(temp), next(begin(temp), min(temp.size(), i + width - 1)), [=](auto& it) {
            if (target == it) {
                it = replacement;
            } else if (target < it) {
                --it;
            } });
    }
    target = replacement;
    return result;
}

int main() {
    const vector<char> rooms = { 0b1101,    0b110,  0b1101, 0b110,  0b1100, 0b101,  0b110,
                                 0b1110,    0b1001, 0b110,  0b1011, 0b1010, 0b1111, 0b1010,
                                 0b1000,    0b101,  0b11,   0b1110, 0b1011, 0b1110, 0b1010,
                                 0b1011,    0b1101, 0b101,  0b1,    0b101,  0b11,   0b1011 };
    const size_t width = 7U;
    auto result = 0;
    vector<int> temp(rooms.size());

    for (size_t i = 0U; i < rooms.size(); ++i) {
        const auto toWest = (rooms[i] & 0b1000) == 0;
        const auto toNorth = (rooms[i] & 0b100) == 0;
        const auto toEast = (rooms[i] & 0b10) == 0;
        const auto toSouth = (rooms[i] & 0b1) == 0;
        const auto west = toWest && temp[i - 1] != 0 ? temp[i - 1] : numeric_limits<int>::max();
        const auto north = toNorth && temp[i - width] != 0 ? temp[i - width] : numeric_limits<int>::max();
        const auto east = toEast && temp[i + 1] != 0 ? temp[i + 1] : numeric_limits<int>::max();

        temp[i] = min({ temp[i] != 0 ? temp[i] : numeric_limits<int>::max(), result + 1, west, north, east });

        if (temp[i] == result + 1) ++result;

        if (toWest) result -= generate(temp, temp[i - 1], width, i);
        if (toNorth) result -= generate(temp, temp[i - width], width, i);
        if (toEast) result -= generate(temp, temp[i + 1], width, i);
        if (toSouth) temp[i + width] = temp[i];
    }

    for (auto it = cbegin(temp); it != cend(temp);) {
        for (auto i = 0; i < width; ++i, ++it) cout << *it << '\t';
        cout << endl;
    }

    cout << endl << result << endl;
}

When compiled on gcc this code gives the error:

Internal compiler error: Segmentation fault it = replacement;

I've tried it locally on gcc 5.1, 5.2, and 5.3 it gives the same compiler error on all of them. Clang seems happy with the code as well as Visual Studio. This is just a compiler bug and not a mistake I've made, right?

Answer 1

The capturing by value of a constant variable in a lambda and the subsequent internal compiler error because of a segmentation fault is a bug in gcc 5.1 - 5.3: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70691

If you need a cloud compiler that has this bug fixed you can use gcc on http://coliru.stacked-crooked.com because it's using gcc 6.1 which has resolved the issue

gcc 5.4 should also have this corrected: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70691#c5
It was released on Jun 3 `16 : https://gcc.gnu.org/gcc-5/