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From: "slyfox at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/98499] [11 Regression] Possibly bad std::string
 initialization in constructors
Date: Sun, 03 Jan 2021 21:50:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98499

--- Comment #4 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
Managed to shrink example even further. Now fails in `037t.fre1`:

```c++
struct string {
  char * _M_buf;
  // local store
  char _M_local_buf[16];

  __attribute__((noinline)) string() : _M_buf(_M_local_buf) {}

  ~string() {
    if (_M_buf !=3D _M_local_buf)
      __builtin_trap();
  }

  string(const string &__str); // no copies
};

// main.cc

__attribute__((noinline)) static string dir_name() { return string(); }
class Importer {
  string base_path;

public:
  __attribute__((noinline)) Importer() : base_path (dir_name()) {}
};

int main() {
  Importer imp;
}
```

```
$ g++-11.0.0 -O2 -std=3Dc++11 main.cc -o a && ./a
Illegal instruction     (core dumped) ./a
$ g++-11.0.0 --param=3Dmodref-max-depth=3D0 -O2 -std=3Dc++11 main.cc -o a &=
& ./a
<ok>
```

It feels like c++'s return-value-optimization somehow misses the PTA.=