On Tue, Mar 17, 2026 at 10:12:03AM +0100, Jakub Jelinek wrote:
> Hi!
>
> On arm*-linux-gnueabi init11.C emits extra diagnostics which the testcase
> doesn't expect.
> E.g. it emits
> init11.C: At global scope:
> init11.C:19:13: error: function of consteval-only type must be declared
> ‘consteval’
> 19 | constexpr C() : i{} {} // { dg-error "function of consteval-only
> type must be declared .consteval." }
> | ^
> init11.C: In constructor ‘constexpr C::C()’:
> init11.C:19:24: error: consteval-only expressions are only allowed in a
> constant-evaluated context
> 19 | constexpr C() : i{} {} // { dg-error "function of consteval-only
> type must be declared .consteval." }
> | ^
> while on most other targets only the first error from these and not
> the second is emitted.
> This is because of targetm.cxx.cdtor_returns_this (), the error is emitted
> on the constructor declaration and then again during
> check_out_of_consteval_use on its body, when walking RETURN_EXPR (which
> normally isn't there).
>
> The following patch arranges diagnostics parity.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux and tested on
> the testcase in cross to armv7-linux-gnueabi, ok for trunk?
Ok by me.
> Though, as I wrote in the PR, I wonder if it makes sense to report
> any errors on bodies of functions for which we've already diagnosed
> function of consteval-only type must be declared ‘consteval’.
> Especially for methods of consteval-only types, any use of this keyword
> will result in an extra error (sure, only the first occurrence in a
> function). But even if a function has only some other consteval-only
> argument and that argument is used somewhere in the body. Though, wonder
> if it is worth trying to improve that now when we don't know if
> consteval-only will not be removed completely or changed significantly.
>
> 2026-03-17 Jakub Jelinek <[email protected]>
>
> PR c++/124474
> * reflect.cc (check_out_of_consteval_use_r): Don't walk subtrees
> of RETURN_EXPR on cdtor_returns_this targets in cdtors.
>
> --- gcc/cp/reflect.cc.jj 2026-03-13 09:13:00.716259526 +0100
> +++ gcc/cp/reflect.cc 2026-03-16 18:05:43.805570930 +0100
> @@ -8246,6 +8246,17 @@ check_out_of_consteval_use_r (tree *tp,
> }
> }
>
> + /* Don't diagnose RETURN_EXPRs in cdtors on cdtor_returns_this
> + target. Those don't exist on other targets. */
> + if (TREE_CODE (t) == RETURN_EXPR
> + && targetm.cxx.cdtor_returns_this ()
> + && (DECL_CONSTRUCTOR_P (current_function_decl)
> + || DECL_DESTRUCTOR_P (current_function_decl)))
> + {
> + *walk_subtrees = false;
> + return NULL_TREE;
> + }
> +
> /* Now check the type to see if we are dealing with a consteval-only
> expression. */
> if (!consteval_only_p (t))
>
> Jakub
>
Marek
