[libcxx-commits] [libcxx] [libc++][ABI BREAK] Make std::pair trivially copyable if its members are (PR #89652)

[Mark de Wever via libcxx-commits]

mordante wrote:

> > I've not really looked closely at the changes. Can you provide a rationale in the commit message why we want to do an unconditional ABI break?
> 
> IMO we should break the ABI if it doesn't actually impact people negatively. The question is mostly whether it will. For this I don't see an obvious failure mode, and it can significantly impact code gen, reducing code size and improving speed (e.g. in `std::copy` or `vector::resize`).

What happens when mixing C++17 and C++20 code, would that work correctly or is there an ABI incompatibility. I would like to have this information in the commit message so the information is in Git; if we wonder in x years why, it's nice to read that in Git. 

I'm not per se against the unconditional ABI break, but I really like to know the scope.



https://github.com/llvm/llvm-project/pull/89652