[PATCH] c++: Fix resolving the address of overloaded pmf [PR96647]

[Patrick Palka]

(Removing libstdc++@gcc.gnu.org from CC list)

On Fri, 28 Aug 2020, Patrick Palka wrote:
> In resolve_address_of_overloaded_function, currently only the second
> pass over the overload set (which considers just the function templates
> in the overload set) checks constraints and performs return type
> deduction when necessary.  But as the testcases below show, we need to
> do this when considering non-template functions during the first pass,
> too.
> 
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/96647
> 	* class.c (resolve_address_of_overloaded_function): Also check
> 	constraints and perform return type deduction when considering
> 	non-template functions in the overload set.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/96647
> 	* g++.dg/cpp0x/auto-96647.C: New test.
> 	* g++.dg/cpp2a/concepts-fn6.C: New test.
> ---
>  gcc/cp/class.c                            | 16 ++++++++++++++++
>  gcc/testsuite/g++.dg/cpp0x/auto-96647.C   | 10 ++++++++++
>  gcc/testsuite/g++.dg/cpp2a/concepts-fn6.C | 10 ++++++++++
>  3 files changed, 36 insertions(+)
>  create mode 100644 gcc/testsuite/g++.dg/cpp0x/auto-96647.C
>  create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-fn6.C
> 
> diff --git a/gcc/cp/class.c b/gcc/cp/class.c
> index 3479b8207d2..c15cb04c654 100644
> --- a/gcc/cp/class.c
> +++ b/gcc/cp/class.c
> @@ -8286,6 +8286,22 @@ resolve_address_of_overloaded_function (tree target_type,
>  	     one, or vice versa.  */
>  	  continue;
>  
> +	/* Constraints must be satisfied. This is done before
> +	   return type deduction since that instantiates the
> +	   function. */
> +	if (!constraints_satisfied_p (fn))
> +	  continue;
> +
> +	if (undeduced_auto_decl (fn))
> +	  {
> +	    /* Force instantiation to do return type deduction.  */
> +	    ++function_depth;
> +	    instantiate_decl (fn, /*defer*/false, /*class*/false);
> +	    --function_depth;
> +
> +	    require_deduced_type (fn);
> +	  }
> +
>  	/* In C++17 we need the noexcept-qualifier to compare types.  */
>  	if (flag_noexcept_type
>  	    && !maybe_instantiate_noexcept (fn, complain))
> diff --git a/gcc/testsuite/g++.dg/cpp0x/auto-96647.C b/gcc/testsuite/g++.dg/cpp0x/auto-96647.C
> new file mode 100644
> index 00000000000..314b2a16ac2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/auto-96647.C
> @@ -0,0 +1,10 @@
> +// PR c++/96647
> +// { dg-do compile { target c++11 } }
> +
> +template<typename>
> +struct Base {
> +  auto f(int) { }
> +  auto f(char) { }
> +};
> +
> +void (Base<void>::*ptr)(int) = &Base<void>::f;
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-fn6.C b/gcc/testsuite/g++.dg/cpp2a/concepts-fn6.C
> new file mode 100644
> index 00000000000..3d7941658d4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-fn6.C
> @@ -0,0 +1,10 @@
> +// PR c++/96647
> +// { dg-do compile { target c++20 } }
> +
> +template<typename T>
> +struct Base {
> +  auto f(int) { }
> +  auto f(int) requires T::fail { static_assert(T::fail); }
> +};
> +
> +void (Base<void>::*ptr)(int) = &Base<void>::f;
> -- 
> 2.28.0.358.g20de7e7e4f
> 
>