aaron.ballman added a comment.
In D90042#2390203 <https://reviews.llvm.org/D90042#2390203>, @flx wrote:
> Thanks for the suggestion, I had never hear of creduce!
Glad to have introduced you to it -- it's a great tool!
> After a bit of trial an error I seem to have found a more minimal example:
>
> namespace std {
> template <typename> class function;
> template <typename a, typename... b> class function<a(b...)> {
> public:
> void operator()(b...);
> };
> } // namespace std
> struct c {
> c();
> c(const c &);
> };
> std::function<void(c &)> f;
> void d() {
> c Orig;
> c Copy = Orig;
> f(Copy);
> }
>
>
> To be frank I can't spot a meaningful difference to the std::function copy we already have.
Aha, I may have spotted it. The call operators have subtly different signatures and the signature we have in our test file is wrong. Note the `&&` in our test file compared to what the standard defines: http://eel.is/c++draft/func.wrap.func#inv which is what's causing the difference here: https://godbolt.org/z/hxfM7P
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