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From: "david at doublewise dot net" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/80039] `constexpr` member function calls in a `constexpr`
 constructor are ignored if the object is defined locally
Date: Tue, 30 Mar 2021 05:49:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D80039

David Stone <david at doublewise dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |david at doublewise dot net

--- Comment #1 from David Stone <david at doublewise dot net> ---
Here's another reproduction

```
struct s {
        int m_value =3D 0;

        constexpr int value() const {
                return m_value;
        }

        constexpr s()
        {
                value();
                m_value =3D 1;
        }
};

constexpr auto x =3D s();
static_assert(x.value() =3D=3D 1);
```

Still a problem on trunk.

This example shows it's not just that side effects are ignored, but also th=
at
the return value is cached. My guess is that there is some code path that
memoizes calls to constexpr functions, replacing them with their return val=
ue,
and that code is getting invoked when it shouldn't be.=