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From: "julien.philippon at epitech dot eu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/104606] New: Regression in comparison operator
 resolution with std::optional
Date: Sat, 19 Feb 2022 16:03:27 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104606

            Bug ID: 104606
           Summary: Regression in comparison operator resolution with
                    std::optional
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: julien.philippon at epitech dot eu
  Target Milestone: ---

Created attachment 52480
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52480&action=3Dedit
Preprocessed file trigering the regression

This code used to compile with G++ 11.1 but does not anymore with G++ 11.2 :

```
#include <optional>
#include <variant>
#include <vector>

struct Value : public std::variant<int, std::vector<Value>> {
    using variant::variant;
};

struct Comparator {
    template <typename T>
    bool operator<=3D(const T &rhs)
    {
        return true;
    }
};

int main()
{
    auto test =3D Comparator() <=3D Value{1};
    auto test2 =3D Comparator() <=3D std::make_optional(Value{1});
}
```

In GCC 11.1 the comparison correctly deduced in the two cases that the lowe=
r or
equal operator of Comparator should be used, but in GCC 11.2, the second
comparison which involve an optional fails to compile.

It looks like GCC is trying to instantiate the three-way comparison operato=
r of
Value, instead of using the operator of Comparator.

Output from g++ -v :

```
Using built-in specs.
COLLECT_GCC=3Dg++
COLLECT_LTO_WRAPPER=3D/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=3D/usr --libdir=3D/u=
sr/lib
--libexecdir=3D/usr/lib --mandir=3D/usr/share/man --infodir=3D/usr/share/in=
fo
--with-bugurl=3Dhttps://bugs.archlinux.org/
--enable-languages=3Dc,c++,ada,fortran,go,lto,objc,obj-c++,d --with-isl
--with-linker-hash-style=3Dgnu --with-system-zlib --enable-__cxa_atexit
--enable-cet=3Dauto --enable-checking=3Drelease --enable-clocale=3Dgnu
--enable-default-pie --enable-default-ssp --enable-gnu-indirect-function
--enable-gnu-unique-object --enable-linker-build-id --enable-lto
--enable-multilib --enable-pgo-build=3Dlto --enable-plugin --enable-shared
--enable-threads=3Dposix --disable-libssp --disable-libstdcxx-pch
--disable-werror --with-build-config=3Dbootstrap-lto
--enable-link-serialization=3D1 gdc_include_dir=3D/usr/include/dlang/gdc
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)
```=