https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121583
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:cddae3e175d078a4eef92260fe31b1144df2116f commit r16-3430-gcddae3e175d078a4eef92260fe31b1144df2116f Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Aug 28 10:51:09 2025 +0200 c++: Fix auto return type deduction with expansion statements [PR121583] The following testcase ICEs during expansion, because cfun->returns_struct wasn't cleared, despite auto being deduced to int. The problem is that check_return_type -> apply_deduced_return_type is called when parsing the expansion stmt body, at that time processing_template_decl is non-zero and apply_deduced_return_type in that case doesn't do the if (function *fun = DECL_STRUCT_FUNCTION (fco)) { bool aggr = aggregate_value_p (result, fco); #ifdef PCC_STATIC_STRUCT_RETURN fun->returns_pcc_struct = aggr; #endif fun->returns_struct = aggr; } My assumption is that !processing_template_decl in that case is used in the sense "the fco function is not a function template", for function templates no reason to bother with fun->returns*struct, nothing will care about that. When returning a type dependent expression in the expansion stmt body, apply_deduced_return_type just won't be called during parsing, but when instantiating the body and all will be fine. But when returning a non-type-dependent expression, while check_return_type will be called again during instantiation of the body, as the return type is no longer auto in that case apply_deduced_return_type will not be called again and so nothing will fix up fun->returns*struct. The following patch fixes that by using !uses_template_parms (fco) check instead of !processing_template_decl. 2025-08-28 Jakub Jelinek <ja...@redhat.com> PR c++/121583 * semantics.cc (apply_deduced_return_type): Adjust fun->returns*_struct when !uses_template_parms (fco) instead of when !processing_template_decl. * g++.dg/cpp26/expansion-stmt23.C: New test. * g++.dg/cpp26/expansion-stmt24.C: New test.
