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

[Patrick Palka <ppalka@redhat.com>]

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..

> 
>   tree lhs = DECL_ARGUMENTS (fndecl);
>   if (is_this_parameter (lhs))
>     lhs = cp_build_fold_indirect_ref (lhs);
>   else
>     lhs = convert_from_reference (lhs);
>   tree ctype = TYPE_MAIN_VARIANT (TREE_TYPE (lhs));
> apparently.
> 
> 	Jakub
> 
>