[C++20] [Modules] Incorrect linkage for in-class static data member

[ChuanqiXu9]

See:

// a.cppm
export module a;
export struct A {
  static constexpr int table[] = {43, 44, 45};
};

According to https://eel.is/c++draft/class.static.data#6, the linkage of A::table should be the same with the A, which has external linkage instead of inline linkage. So we should be able to see its definition in a.o. But it is not true:

clang++ -std=c++20 a.cppm -emit-llvm -S -o -

Then we can't see the definition for A::table. It shows we didn't handle the linkage for A::table correctly.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: Chuanqi Xu (ChuanqiXu9)

See:

// a.cppm
export module a;
export struct A {
  static constexpr int table[] = {43, 44, 45};
};

According to https://eel.is/c++draft/class.static.data#6, the linkage of A::table should be the same with the A, which has external linkage instead of inline linkage. So we should be able to see its definition in a.o. But it is not true:

clang++ -std=c++20 a.cppm -emit-llvm -S -o -

Then we can't see the definition for A::table. It shows we didn't handle the linkage for A::table correctly.

[ChuanqiXu9]

Wait. This is not a clear problem. I just noticed that there is no inline linkage in the spec. inline linkage is a concept in clang. So we can't explain the spec with the concept in clang. Then while we can say the current behavior doesn't violate the spec, there are some related discussion in itanium-cxx-abi/cxx-abi#170.