<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/55315>55315</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang++ compiler error about static constexpr member function
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          akr-akari
      </td>
    </tr>
</table>

<pre>
    The code is as follows.
```
struct Test
{
    static constexpr void foo1() noexcept
    {
        fooImpl(2022);
    }

    static constexpr void foo2() noexcept
    {
        fooImpl(3.14);
    }

    template<class T>
    static constexpr void fooImpl(T value) noexcept
    {
    }
};

int main()
{
    Test t;
    t.foo1();
    t.foo2();
}
```
In gcc, it compiles successfully. But in clang, the compilation fails and the output is as follows.
```
>clang++ main.cc -omain.exe
main.cc:19:27: warning: inline function 'Test::fooImpl<int>' is not defined
      [-Wundefined-inline]
    static constexpr void fooImpl(T value) noexcept
                          ^
main.cc:10:9: note: used here
        fooImpl(2022);
        ^
main.cc:19:27: warning: inline function 'Test::fooImpl<double>' is not defined
      [-Wundefined-inline]
    static constexpr void fooImpl(T value) noexcept
                          ^
main.cc:15:9: note: used here
        fooImpl(3.14);
        ^
2 warnings generated.
C:/Users/XIANG/winlibs/mingw64/bin/ld: C:/Users/XIANG/AppData/Local/Temp/main-640e60.o:main.cc:(.text$_ZN4Test4foo1Ev[_ZN4Test4foo1Ev]+0xa): undefined reference to `void Test::fooImpl<int>(int)'
C:/Users/XIANG/winlibs/mingw64/bin/ld: C:/Users/XIANG/AppData/Local/Temp/main-640e60.o:main.cc:(.text$_ZN4Test4foo2Ev[_ZN4Test4foo2Ev]+0xd): undefined reference to `void Test::fooImpl<double>(double)'
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
```
But I put `fooImpl()` at the top and it compiles successfully. 

The code is as follows.
```
struct Test
{
    template<class T>
    static constexpr void fooImpl(T value) noexcept
    {
    }

    static constexpr void foo1() noexcept
    {
        fooImpl(2022);
    }

    static constexpr void foo2() noexcept
    {
        fooImpl(3.14);
    }
};

int main()
{
    Test t;
    t.foo1();
    t.foo2();
}
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzlVluv4jYQ_jXhxSIKDgnhIQ9cDtWRqn2iatWXleNMwD3GjmwH2H_fsQkKlHO6Z7crdVeLomSIPbdvZj6n0vWncrsHwnUNRFjCLGm0lPpk4yhZR8kiypP-Cn-tMx13ZAvW9euz5UUg-LOOOcHRmLIOzq0hRy1qNKgnES0iOidKw5lD6waVO33_w93Ph1aiAk0oRaUoXd5uX_d-P--Ufo3TNJ5M3-HUAW5nDqJ0xSWzlmyj9OkdMfVetuTIZAfviG7wjcI1qMtdKEcOTKhLmq-Uw1eJuLtUXDxU43GB_mNhcH7fBc-K7DiP6IoIh0keWiHBEttxDtY2nZSfYrLsHBGKIDpq53e60GV-K0KjFWmYkNhvqg4runOtV_h8ByLOvc0lXgGAmHMy1kGCM1y29e-jdDHBfBZ0hjdyYkYJVEVRKCkUkKZTPIQT0Vlo6hQdLK6FSleIsS8snfnQlHakhgb16tv2ibLl-PdO9Svji-UoW3-jdnj9F2VPD4kmePPJ-kDBPzsLNdmDgS8Zsbes_xcYa91VEn4cJLMvRvI13rizTq-wWbIDBQbJo-47fOXhopvfLBiLzz-eFx9-wefJ51_5NwdUO-Vof1P5cd_I2sf0htqibdfMMZR-1ZxhbJstkpW3gvmN82kCeRJr1B3yxfhjhNNFdPrxzw9TX8Gp54mnI1bk4c0a5y45s5AtInMtFzHQIECKA3Ga4LyG0vzbUBVeQCvYVd81DvQBBzrgUH89DjdTUfTyDRo3LOftgzHaeAFn4gWM59KDZ0_Po-j0JNyewDnwMR7lE5zEApuWjI8-Cgt4uqsj4uCndDgt7qnVU_Yz8TyMr4bW9tvzhDAXmNrpNrD228x_e0Z9u2-L_-HE_Xm-a76Lb4tRXab1PJ2zkRNOQrm6Oeb7VjOXMSCswg-GR4QOcKhwz_U0GnVGlnvnWnthCLx2OCZdFaM5Tx_yeH2MW6P_Ao6TvxHWduCJJMvSSTbalylGVdU0y1mecqD1LE8LPi9oXjUsKybpSLIKpC2RIyJKFZxIMIEycsRIlL7eSZbMknk2pUmc5JNJUcxmTV7MswaPGmQihFrGPo5Ym93IlCGkqttZXJTCOjssYuuLnQII7tA-69xem5K9mDF7YUaMgvMyBP83bOVolg">