[PATCH] c++: Don't synthesize sfk_comparison method multiple times [PR94907]

[Jason Merrill]

On 5/5/20 3:15 AM, Jakub Jelinek wrote:
> Hi!
> 
> On the following testcase we ICE, because synthesize_method is called twice
> on the same sfk_comparison method fndecl, the first time it works fine
> because start_preparsed_function in that case sets both
> current_function_decl and cfun, but second time it is called it only sets
> the former and keeps cfun NULL, so we ICE when trying to store
> current_function_returns_value.
> I think it is just wrong to call synthesize_method multiple times, and most
> synthesize_method callers avoid that by not calling it if DECL_INITIAL is
> already set, so this patch does that too.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK for trunk and 10.x.

> 2020-05-05  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/94907
> 	* method.c (defaulted_late_check): Don't call synthesize_method
> 	on constexpr sfk_comparison if it has been called on it already.
> 
> 	* g++.dg/cpp2a/spaceship-synth8.C: New test.
> 
> --- gcc/cp/method.c.jj	2020-04-29 09:00:24.525851362 +0200
> +++ gcc/cp/method.c	2020-05-04 15:41:14.016544034 +0200
> @@ -2939,7 +2939,7 @@ defaulted_late_check (tree fn)
>       {
>         /* If the function was declared constexpr, check that the definition
>   	 qualifies.  Otherwise we can define the function lazily.  */
> -      if (DECL_DECLARED_CONSTEXPR_P (fn))
> +      if (DECL_DECLARED_CONSTEXPR_P (fn) && !DECL_INITIAL (fn))
>   	synthesize_method (fn);
>         return;
>       }
> --- gcc/testsuite/g++.dg/cpp2a/spaceship-synth8.C.jj	2020-05-04 15:34:02.106002574 +0200
> +++ gcc/testsuite/g++.dg/cpp2a/spaceship-synth8.C	2020-05-04 15:33:51.654158860 +0200
> @@ -0,0 +1,12 @@
> +// PR c++/94907
> +// { dg-do compile { target c++2a } }
> +
> +namespace std { struct strong_ordering { }; }
> +
> +struct E;
> +struct D {
> +  virtual std::strong_ordering operator<=>(const struct E&) const = 0;
> +};
> +struct E : D {
> +  std::strong_ordering operator<=>(const E&) const override = default;
> +};
> 
> 	Jakub
>