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From: "gene at staubsaal dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/115180] New: [regression] free-nonheap-object on
 std::vector usage
Date: Tue, 21 May 2024 18:11:47 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.1.1
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: gene at staubsaal dot de
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115180

            Bug ID: 115180
           Summary: [regression] free-nonheap-object on std::vector usage
           Product: gcc
           Version: 14.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gene at staubsaal dot de
  Target Milestone: ---

Compiler: gcc (GCC) 14.1.1
Compile flags: -std=3Dc++20 -O3 -Wfree-nonheap-object

The following code produces an "-Wfree-nonheap-object" warning, which doesn=
't
happen with '-O2' or using an older version of gcc.
This seems to be a false warning. (Or maybe even some false optimization go=
ing
on?)

```
#include <cassert>
#include <vector>


// Since K+1 the returned vector has size() >=3D 1
inline auto f(size_t N, size_t K) {
    return std::vector<std::vector<size_t>>(K+1, std::vector<size_t>(N, 0));
}

// create another vector, but derive size from the previous vector
inline auto g(std::vector<std::vector<size_t>> const& v1) {
    size_t const K =3D v1.size() - 1;
    size_t const N =3D v1[0].size();
    return std::vector<std::vector<size_t>>(K+1, std::vector<size_t>(N, 0));
}

struct S {
    std::vector<size_t> v1;
    std::vector<size_t> v2;
    // v1, v2always have the same length
};

auto h(size_t N, size_t K) {
    assert(N>0);
    assert(N >=3D K);

    auto v1 =3D f(N, K);
    auto v2 =3D g(v1);

    auto ss =3D std::vector<S>{};
    for (size_t i{0}; i < v1.size(); ++i) {
        ss.emplace_back(S{v1[i], {}});
    }

    for (auto& s : ss) {
        s.v1.back() +=3D 1;
    }

    return ss;
}

auto all =3D h(4, 3);
```
For convenience a link to godbolt: https://godbolt.org/z/dPj1YYf7x=