On Tue, 28 Sep 2021, Jakub Jelinek via Gcc-patches wrote:
> Hi!
>
> The testcases in the patch are either miscompiled or ICE with checking,
> because the defaulted operator== is synthetized too early (but only if
> constexpr), when the corresponding class type is still incomplete type.
> The problem is that at that point the bitfield FIELD_DECLs still have as
> TREE_TYPE their underlying type rather than integral type with their
> precision and when layout_class_type is called for the class soon after
> that, it changes those types but the COMPONENT_REFs type stay the way
> that they were during the operator== synthetize_method type and the
> middle-end is then upset by the mismatch of types.
> As what exact type will be given isn't just a one liner but quite long code
> especially for over-sized bitfields, I think it is best to just not
> synthetize the comparison operators so early (the defaulted_late_check
> change) and call defaulted_late_check for them once again as soon as the
> class is complete.
Nice, this might also fix PR98712.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2021-09-28 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/102490
> * method.c (defaulted_late_check): Don't synthetize constexpr
> defaulted comparisons if context is still incomplete type.
> (finish_struct_1): Call defaulted_late_check again for defaulted
> comparisons.
>
> * g++.dg/cpp2a/spaceship-eq11.C: New test.
> * g++.dg/cpp2a/spaceship-eq12.C: New test.
>
> --- gcc/cp/method.c.jj 2021-09-15 08:55:37.563497558 +0200
> +++ gcc/cp/method.c 2021-09-27 13:48:12.139271830 +0200
> @@ -3160,8 +3160,11 @@ defaulted_late_check (tree fn)
> if (kind == sfk_comparison)
> {
> /* If the function was declared constexpr, check that the definition
> - qualifies. Otherwise we can define the function lazily. */
> - if (DECL_DECLARED_CONSTEXPR_P (fn) && !DECL_INITIAL (fn))
> + qualifies. Otherwise we can define the function lazily.
> + Don't do this if the class type is still incomplete. */
> + if (DECL_DECLARED_CONSTEXPR_P (fn)
> + && !DECL_INITIAL (fn)
> + && COMPLETE_TYPE_P (ctx))
> {
According to the function comment for defaulted_late_check, won't
COMPLETE_TYPE_P (ctx) always be false here?
> /* Prevent GC. */
> function_depth++;
> --- gcc/cp/class.c.jj 2021-09-03 09:46:28.801428380 +0200
> +++ gcc/cp/class.c 2021-09-27 14:07:03.465562255 +0200
> @@ -7467,7 +7467,14 @@ finish_struct_1 (tree t)
> for any static member objects of the type we're working on. */
> for (x = TYPE_FIELDS (t); x; x = DECL_CHAIN (x))
> if (DECL_DECLARES_FUNCTION_P (x))
> - DECL_IN_AGGR_P (x) = false;
> + {
> + /* Synthetize constexpr defaulted comparisons. */
> + if (!DECL_ARTIFICIAL (x)
> + && DECL_DEFAULTED_IN_CLASS_P (x)
> + && special_function_p (x) == sfk_comparison)
> + defaulted_late_check (x);
> + DECL_IN_AGGR_P (x) = false;
> + }
> else if (VAR_P (x) && TREE_STATIC (x)
> && TREE_TYPE (x) != error_mark_node
> && same_type_p (TYPE_MAIN_VARIANT (TREE_TYPE (x)), t))
> --- gcc/testsuite/g++.dg/cpp2a/spaceship-eq11.C.jj 2021-09-27
> 14:20:04.723713371 +0200
> +++ gcc/testsuite/g++.dg/cpp2a/spaceship-eq11.C 2021-09-27
> 14:20:20.387495858 +0200
> @@ -0,0 +1,43 @@
> +// PR c++/102490
> +// { dg-do run { target c++20 } }
> +
> +struct A
> +{
> + unsigned char a : 1;
> + unsigned char b : 1;
> + constexpr bool operator== (const A &) const = default;
> +};
> +
> +struct B
> +{
> + unsigned char a : 8;
> + int : 0;
> + unsigned char b : 7;
> + constexpr bool operator== (const B &) const = default;
> +};
> +
> +struct C
> +{
> + unsigned char a : 3;
> + unsigned char b : 1;
> + constexpr bool operator== (const C &) const = default;
> +};
> +
> +void
> +foo (C &x, int y)
> +{
> + x.b = y;
> +}
> +
> +int
> +main ()
> +{
> + A a{}, b{};
> + B c{}, d{};
> + C e{}, f{};
> + a.b = 1;
> + d.b = 1;
> + foo (e, 0);
> + foo (f, 1);
> + return a == b || c == d || e == f;
> +}
> --- gcc/testsuite/g++.dg/cpp2a/spaceship-eq12.C.jj 2021-09-27
> 14:20:12.050611625 +0200
> +++ gcc/testsuite/g++.dg/cpp2a/spaceship-eq12.C 2021-09-27
> 14:20:39.633228602 +0200
> @@ -0,0 +1,5 @@
> +// PR c++/102490
> +// { dg-do run { target c++20 } }
> +// { dg-options "-O2" }
> +
> +#include "spaceship-eq11.C"
>
> Jakub
>
>
