[PATCH] c++: Fix up synthetization of defaulted comparison operators on classes with bitfields [PR102490]

[Jakub Jelinek]

On Tue, Sep 28, 2021 at 01:25:13PM -0400, Patrick Palka via Gcc-patches wrote:
> On Tue, 28 Sep 2021, Jakub Jelinek wrote:
> 
> > On Tue, Sep 28, 2021 at 06:49:38PM +0200, Jakub Jelinek via Gcc-patches wrote:
> > > On Tue, Sep 28, 2021 at 12:44:58PM -0400, Patrick Palka wrote:
> > > > Ah yeah, sorry for the noise, I misunderstood the function comment.
> > > > 
> > > > On a related note I think 'ctx' can also be a NAMESPACE_DECL here in
> > > > the case of a defaulted non-member operator<=> (as in the below), for
> > > > which I'd expect the added COMPLETE_TYPE_P check to crash, but it looks
> > > > like in this case DECL_INITIAL is error_mark_node instead of NULL_TREE
> > > > so a crash is averted.  If anyone else was wondering...
> > > > 
> > > >   struct A {
> > > >     friend constexpr bool operator==(const A&, const A&);
> > > >   };
> > > > 
> > > >   constexpr bool operator==(const A&, const A&) = default;
> > > 
> > > That means maybe ctx isn't the right way to get at the type and we
> > > should look it up from the first argument's type?
> > > I guess I'll look at where the build_comparison_op takes it from...
> 
> I suspect this synthesize_method call from defaulted_late_check is
> really only needed when operator<=> has been defaulted inside the class
> definition, because out-of-class defaulted definitions generally already
> get eagerly synthesized IIUC.  So it might be fine to keep using ctx if
> we also check DECL_DEFAULTED_IN_CLASS_P in defaulted_late_check.  But
> Jason knows for sure..

Indeed, cp_finish_decl has:
8333			  /* An out-of-class default definition is defined at
8334			     the point where it is explicitly defaulted.  */
8335			  if (DECL_DELETED_FN (decl))
8336			    maybe_explain_implicit_delete (decl);
8337			  else if (DECL_INITIAL (decl) == error_mark_node)
8338			    synthesize_method (decl);

	Jakub