Hi! I am currently learning about pragmas in C++. I know that there are a lot of different pragmas you can do to speedup your program, e.g. #pragma GCC optimize("O3,unroll-loops") and #pragma GCC target("avx2"). However, I have some questions:

1. When I include #pragma GCC target("avx2"), I get this error

In file included from C:/mingw64/include/c++/14.2.0/string:43,
                 from C:/mingw64/include/c++/14.2.0/bitset:52,
                 from C:/mingw64/include/c++/14.2.0/x86_64-w64-mingw32/bits/stdc++.h:52,
                 from c:\Users\minhduc\Documents\comp\596B.cpp:5:
C:/mingw64/include/c++/14.2.0/bits/allocator.h: In destructor 'constexpr std::__cxx11::basic_string<char>::_Alloc_hider::~_Alloc_hider()':
C:/mingw64/include/c++/14.2.0/bits/allocator.h:182:7: error: inlining failed in call to 'always_inline' 'constexpr std::allocator< <template-parameter-1-1> >::~allocator() noexcept [with _Tp = char]': target specific option mismatch
  182 |       ~allocator() _GLIBCXX_NOTHROW { }
      |       ^
In file included from C:/mingw64/include/c++/14.2.0/string:54:
C:/mingw64/include/c++/14.2.0/bits/basic_string.h:186:14: note: called from here
  186 |       struct _Alloc_hider : allocator_type // TODO check __is_final

What is weird is that the pragma works when I run it on a smaller file. E.g. this code runs perfectly well with no errors:

#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2")
#include <bits/stdc++.h>
using namespace std;

int main() { cout << "idk"; }

but then this code doesn't (it throws that large error above):

#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2")

#define __USE_MATH_DEFINES
#include <bits/stdc++.h>

#include <cmath>

#define endl '\n'
using namespace std;
using ll = long long;
using ull = unsigned long long;

const ll mod = 1e9 + 7, mod2 = 998244353, maxn = 1e6 + 1, maxn2 = 2e3 + 1;
// all the mods are primes!
template <typename T>
inline void dbgar(T *tr, ll n) {
    for (int i = 1; i <= n; i++) cout << tr[i] << ' ';
    cout << endl;
}

ll n, t, k, m, a, b, z, q, c, p, d;
long double g, u, w;
char ch;
ll ar[maxn], br[maxn], cr[maxn], dr[maxn];
string s, x;

int __tests__ = 1;
bool __MT__ = 0;

inline void preprocess() {}

inline void solve() {
    cin >> n;
    t = 0;
    z = 0;
    for (int i = 1; i <= n; i++) {
        cin >> a;
        z += abs(a - t);
        t = a;
    }
    cout << z;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout << fixed << setprecision(20);
    preprocess();
    if (__MT__) cin >> __tests__;
    for (int __jiji__ = 1; __jiji__ <= __tests__; __jiji__++) solve();
    return 0;
}

I downloaded my g++ compiler from Winlibs, with version GCC 14.2.0 (with POSIX threads) + LLVM/Clang/LLD/LLDB 19.1.1 + MinGW-w64 12.0.0 UCRT - release 2 (LATEST), if it helps.

Does anyone know what is the problem? My laptop is rather new (and g++ -mavx2 <random file> works), so I doubt there's anything wrong with the instruction sets stuff. Also for the large code above the issue seems to be from the avx2 pragma line, as removing it makes the code work normally again. Does anyone have any idea what is the possible issue? Thanks in advance!

Problem:

Given a string $$$S$$$ containing only digits from $$$1$$$ to $$$9$$$, with length at most $$$5 * 10 ^ 5$$$. Find all pairs $$$(L, R)$$$ such that the substring of $$$S$$$ from $$$L$$$ to $$$R$$$ forms a number divisible by $$$2019$$$.

Problem source (Vietnamese): https://lqdoj.edu.vn/problem/mult2019

My idea for this problem is to try and evaluate all substrings and check if they are divisible, but of course that would be too long. Other than that I am pretty stuck.

I would love to know if there are better ideas for this problem. Thanks in advance!