Re: [PATCH] c++: conditional noexcept-spec on defaulted comparison op [PR96242]

[Jason Merrill <jason@redhat.com>]

On 2/3/22 14:58, Patrick Palka wrote:
> When synthesizing a defaulted comparison op from
> maybe_instantiate_noexcept, we seem to be forgetting to instantiate the
> noexcept-spec afterwards.

Hmm, there shouldn't be any need to instantiate the noexcept-spec 
afterwards, it should have been set by ~comp_info.

> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk and perhaps 11?
> 
> 	PR c++/96242
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (maybe_instantiate_noexcept): Keep going after
> 	successfully synthesizing a DECL_MAYBE_DELETED fn.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/spaceship-synth15.C: New test.
> ---
>   gcc/cp/pt.cc                                  |  3 ++-
>   .../g++.dg/cpp2a/spaceship-synth15.C          | 22 +++++++++++++++++++
>   2 files changed, 24 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 6dd64101ced..03345ed3ed3 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -25986,7 +25986,8 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
>         ++function_depth;
>         maybe_synthesize_method (fn);
>         --function_depth;
> -      return !DECL_MAYBE_DELETED (fn);
> +      if (DECL_MAYBE_DELETED (fn))
> +	return false;
>       }
>   
>     tree fntype = TREE_TYPE (fn);
> diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C
> new file mode 100644
> index 00000000000..00ea6c10474
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C
> @@ -0,0 +1,22 @@
> +// PR c++/96242
> +// { dg-do compile { target c++20 } }
> +
> +#include <compare>
> +
> +template<bool B>
> +struct X {
> +  auto operator<=>(const X&) const noexcept(B) = default;
> +  bool operator==(const X&) const noexcept(!B) = default;
> +};
> +
> +X<true> x_t;
> +static_assert(noexcept(x_t <=> x_t));
> +static_assert(noexcept(x_t < x_t));
> +static_assert(!noexcept(x_t == x_t));
> +static_assert(!noexcept(x_t != x_t));
> +
> +X<false> x_f;
> +static_assert(!noexcept(x_f <=> x_f));
> +static_assert(!noexcept(x_f < x_f));
> +static_assert(noexcept(x_f == x_f));
> +static_assert(noexcept(x_f != x_f));