[llvm-bugs] [Bug 37918] New: When compiling with `-fopenmp` clang will under certain circumstances not produce symbols for const or constexpr static data members.

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37918

            Bug ID: 37918
           Summary: When compiling with `-fopenmp` clang will under
                    certain circumstances not produce symbols for const or
                    constexpr static data members.
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: chris at detrino.org
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org

This seems to happen when the following is true:

- A const or constexpr static data member is declared in a class.
- The data member is ODR-used before its definition is seen.
- The TU is compiled with `-fopenmp`
- This all happens in the global namespace.

A reduced test-case:

    // Section A - Define a class with a static constexpr data member.
    struct Foo {
      static constexpr int bar = 1;
    };

    // Section B - ODR-use the data member.
    void F(const int&);
    void Test() { F(Foo::bar); }

    // Section C - Define the data member.
    constexpr int Foo::bar;

In this example, the `Foo::bar` symbol will not be produced in the output
.s/.o. This can be worked around by moving `Section C` before `Section B`. See
https://godbolt.org/g/LrzUvY for a live demo.

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