从最后一个往回走一步是谁

运行下面这段程序：

#include <iostream>
#include <string>
#include <utility>
#include <vector>
using namespace std;

struct DNode {
    string name;
    DNode* next = nullptr;
    DNode* prev = nullptr;
};

pair<DNode*, DNode*> dbuild(const vector<string>& names) {
    DNode* head = nullptr;
    DNode* tail = nullptr;
    for (const string& x : names) {
        DNode* nd = new DNode{x};
        if (head == nullptr) {
            head = nd;
        } else {
            tail->next = nd;
            nd->prev = tail;
        }
        tail = nd;
    }
    return {head, tail};
}

int main() {
    auto [head, tail] = dbuild({"阿岚", "小满", "阿泰", "南风"});
    cout << tail->prev->name << endl;
}

（本题用 g++ -std=c++17 -O0 编译。）