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:
- 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!
