Meinersbur wrote:

> I don’t personally think that the flang driver should ever attempt to link a 
> C++ library of any kind. FWIW while there’s no stdlib option to consider in 
> their case, g++ will never auto link the gfortran runtimes and gfortran will 
> never auto link libstdc++

gfortran doesn't have a flag that means "use this C++ standard library". 
Without this PR, Flang doesn't either which would be fine with me. OP would 
need to fix their build system.

With this PR, `flang --help` will list an option `-stdlib` with the help text 
"C++ standard library to use". But it doesn't do anything. It feels like it 
would be ignoring `-lc++`.


> If we were to do things this way, what should flang do if no -stdlib flag is 
> provided? Should it link the default C++ stdlib as clang++ does, or break 
> with clang++ and not link any C++ stdlib if nothing is provided? Both would 
> be surprising behavior in my opinion, and both would also risk breaking the 
> existing cmake support.

No `-stdlib` means no linking to any C++ standard library for Flang, no change 
of behavior without the flag. It also does not break cmake support since it 
never passes `-stdlib` by itself. Just asking for the flag's behavior to match 
its description. 


https://github.com/llvm/llvm-project/pull/110598
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