<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64777>64777</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [C++20] [constexpr] virtual member function template specialisation compilation error
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          pkeir
      </td>
    </tr>
</table>

<pre>
    The C++20 code below fails to compile with Clang trunk (GCC and MSVC compile fine). Removing either both `constexpr` qualifiers; or the `virtual` specifier will remove the error.

```cpp
template <typename T> 
struct Foo 
{ 
  constexpr 
  virtual 
  void m() { } 
}; 
 
template<> 
constexpr 
void Foo<int*>::m() { }
```

The invocation and error message are below:

```
$ clang++ -std=c++20 -c test.cpp 
test.cpp:15:17: error: explicit specialization of 'm' after instantiation
void Foo<int*>::m() { }
 ^
test.cpp:15:6: note: implicit instantiation first required here
void Foo<int*>::m() { }
     ^
1 error generated.
```
</pre>
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