https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110102
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
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Target Milestone|13.2 |---
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Arthur O'Dwyer from comment #4)
> My first, reduced, example, where `std::list<A> v = {1,2,3}` is accepted for
> move-only type `A`, is 100% a bug and should be fixed. But that is easy to
> fix.
It's pedantically a bug, but only because of the suboptimal specified
initializer_list semantics. Just looking at that line I expect a list of As
initialized from integers; I don't expect that initialization to involve an
unnecessary copy.
It's also unfortunate that initialization from a prvalue initializer_list can't
use the A move constructor.
> struct NthPrime { constexpr NthPrime(int); ... };
> std::vector<NthPrime> primes = {1,2,3,4,5,6};
> Here we *want* to make an initializer_list<NthPrime> backed by a static
> array of NthPrime at compile time. If we make an initializer_list<int>, then
> we'll have to run the NthPrime(int) constructor at runtime, and that's
> expensive.
> I tried out this example on Godbolt and the optimizer made the correct
> choice in this specific case, so that's good.
Right, we don't do this transformation if the initializer_list backing array
would be constant.
