On 2/3/26 5:09 PM, Jakub Jelinek wrote:
Hi!We emit weird diagnostics on the following testcase in C++11. If it is not a template, maybe_save_constexpr_fundef calls first if (!is_valid_constexpr_fn (fun, complain)) return; (which doesn't fail) and then tree massaged = massage_constexpr_body (fun, DECL_SAVED_TREE (fun)); if (massaged == NULL_TREE || massaged == error_mark_node) { if (!DECL_CONSTRUCTOR_P (fun) && complain) error ("body of %<constexpr%> function %qD not a return-statement", fun); return; } which diagnoses it and if even that would succeed, go on with bool potential = potential_rvalue_constant_expression (massaged); if (!potential && complain) require_potential_rvalue_constant_expression_fncheck (massaged); In templates, maybe_save_constexpr_fundef returns early: if (processing_template_decl || cp_function_chain->invalid_constexpr || (DECL_CLONED_FUNCTION_P (fun) && !DECL_DELETING_DESTRUCTOR_P (fun))) return; and then it is called again during instantiation. But in that case DECL_GENERATED_P (fun) is true and so we silently return on errors without diagnosing them: bool complain = !DECL_GENERATED_P (fun) && !implicit; Now, when we actually try to constexpr evaluate those (if at all), we emit an error and then 'constexpr ...' is not usable as a 'constexpr' function because: message and then explain_invalid_constexpr_fn tries to diagnose the errors by calling is_valid_constexpr_fn (fun, true) and require_potential_rvalue_constant_expression (massaged). So it diagnoses those 2 cases, but misses the one where massaged was NULL or error_mark_node for a non-constructor, so after the because: there is no reason emitted. The following patch diagnoses even that. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2026-02-03 Jakub Jelinek <[email protected]> PR c++/123889 * constexpr.cc (explain_invalid_constexpr_fn): Diagnose NULL or error_mark_node massaged on non-constructor. * g++.dg/cpp0x/constexpr-123889.C: New test. --- gcc/cp/constexpr.cc.jj 2026-01-31 10:16:31.950164802 +0100 +++ gcc/cp/constexpr.cc 2026-02-02 14:35:43.506094992 +0100 @@ -1116,6 +1116,10 @@ explain_invalid_constexpr_fn (tree fun) else body = DECL_SAVED_TREE (fun); tree massaged = massage_constexpr_body (fun, body); + if ((massaged == NULL_TREE || massaged == error_mark_node) + && !DECL_CONSTRUCTOR_P (fun)) + error ("body of %<constexpr%> function %qD not a return-statement", + fun); require_potential_rvalue_constant_expression (massaged); if (DECL_CONSTRUCTOR_P (fun))
Since we have this DECL_CONSTRUCTOR_P check already, let's make the new code an else?
OK either way. Jason
