ClaytonKnittel wrote:
> The original case where I got hit with this was some abseil map, the type
> without debugging information was std::pair.
>
>
>
> libstdc++ has these constructors for pair:
>
>
>
> ```c++
>
> constexpr pair(const pair&) = default; ///< Copy constructor
>
> constexpr pair(pair&&) = default; ///< Move constructor
>
>
>
> template<typename... _Args1, typename... _Args2>
>
> _GLIBCXX20_CONSTEXPR
>
> pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
>
>
>
> template<typename... _Args1, size_t... _Indexes1,
>
> typename... _Args2, size_t... _Indexes2>
>
> _GLIBCXX20_CONSTEXPR
>
> pair(tuple<_Args1...>&, tuple<_Args2...>&,
>
> _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>);
>
>
>
> constexpr
>
> explicit(__not_<__and_<__is_implicitly_default_constructible<_T1>,
>
> __is_implicitly_default_constructible<_T2>>>())
>
> pair()
>
> noexcept(is_nothrow_default_constructible_v<_T1>
>
> && is_nothrow_default_constructible_v<_T2>)
>
> requires is_default_constructible_v<_T1>
>
> && is_default_constructible_v<_T2>
>
> : first(), second()
>
> { }
>
>
>
> ```
>
>
>
> I see that abseil uses the piecewise_construct constructor, which at the
> point of the template definition, is declared but not defined. It is defined
> later.
>
>
>
> Could it be that at the point the code checks whether the constexpr
> constructor is defined or not, the compiler hasn't instantiated the
> constructor definition?
>
>
>
>
Could you write a minimal repro that compiles but lacks debug info? I'm happy
to try to fix-forward, and if we can't we can roll back the original change.
https://github.com/llvm/llvm-project/pull/221566
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