Hello Patrick,
On Wed, May 03 2023, Patrick Palka via Gcc-patches wrote:
>
[...]
>
> Subject: [PATCH] c++: potentiality of templated memfn call [PR109480]
>
> Here we're incorrectly deeming the templated call a.g() inside b's
> initializer as potentially constant, despite g being non-constexpr,
> which leads to us wastefully instantiating the initializer ahead of time,
> which incidentally tiggers a bug in access checking deferral (to be
> fixed by the subsequent patch).
>
> This patch fixes this by calling get_fns earlier during CALL_EXPR
> potentiality checking so that we're able to extract a FUNCTION_DECL out
> of a templated member function call (whose overall is typically a
> COMPONENT_REF) and to the usual checking if the called function is
> constexpr etc.
>
> In passing, I noticed potential_constant_expression_1's special handling
> of the object argument of a non-static member function call is effectively
> the same as the generic argument handling a few lines later. So this
> patch just gets rid of this special handling; otherwise we'd have to adapt
> it to handle templated versions of such calls.
>
> PR c++/109480
>
> gcc/cp/ChangeLog:
>
> * constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
> Reorganize to call get_fns sooner. Remove special handling of
> the object argument of a non-static member function call. Remove
> dead store to 'fun'.
>
This patch makes g++ no longer accept the following, complaining that
get_subsys is non-constexpr (with just -std=c++17 -S), which is of
course auto-reduced from a much larger source file from Ceph:
----------------------------------- 8< -----------------------------------
struct {
void get_subsys();
} PriorSet_dpp;
struct PriorSet {
template <typename> PriorSet();
};
template <typename> PriorSet::PriorSet() {
[](auto cctX) { cctX.template should_gather<PriorSet_dpp.get_subsys()>; };
}
----------------------------------- 8< -----------------------------------
I assume that is intentional and am actually somewhat surprised it was
accepted before, but can you please confirm?
Thanks,
Martin
