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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110150] std::optional inside template leads to long
 compilation time
Date: Tue, 06 Jun 2023 21:52:23 +0000
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X-Bugzilla-Component: c++
X-Bugzilla-Version: 12.1.0
X-Bugzilla-Keywords: compile-time-hog
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110150

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |compile-time-hog

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am not shocked because even this takes some time (not as much as the orig=
inal
one):
```
template <typename T>
struct optional
{
        T a;
        optional();
        template<typename O>
        optional(const optional<O>&);
};

template<typename T>
void f(T x)
{
    f(optional<T>(x));
}
int main()
{
   // using std::optional;
    optional<int> x;
    f(x);
    return 0;
}
```

There is an enable if on the optional constructor in the std::optional case
which makes the time increase even more.

I doubt there is much to be optimized here except maybe lowering the templa=
te
depth limit (from the current 900, that is -ftemplate-depth=3D900 is the
default).=