[Bug c++/126354] Returning from [[noreturn]] function not rejected in constant evaluation

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126354

--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <[email protected]>:

https://gcc.gnu.org/g:571aae1dc596ec58bca11534800a857109dce498

commit r17-2664-g571aae1dc596ec58bca11534800a857109dce498
Author: Jakub Jelinek <[email protected]>
Date:   Thu Jul 23 15:42:10 2026 +0200

    c++: Diagnose return from [[noreturn]] function during constant evaluation
[PR126354]

    This PR complains about g++ not diagnosing return from [[noreturn]]
    function (which is UB) during constant evaluation.

    This patch diagnoses that.
    I haven't included the [[noreturn]] function name in the diagnostics
    as it is printed in the context:
    /home/jakub/src/gcc/gcc/testsuite/g++.dg/cpp1y/pr126354.C:18:24:   in
'constexpr' expansion of 'bar()'
    /home/jakub/src/gcc/gcc/testsuite/g++.dg/cpp1y/pr126354.C:15:7:   in
'constexpr' expansion of 'foo(false)'
    /home/jakub/src/gcc/gcc/testsuite/g++.dg/cpp1y/pr126354.C:15:7: error:
'[[noreturn]]' call returns
    But if you think it is better to emit
    error ("%<[[noreturn]]%> %qD call returns", fun);
    instead, I can certainly do that.

    2026-07-23  Jakub Jelinek  <[email protected]>

            PR c++/126354
            * constexpr.cc (cxx_eval_call_expression): Diagnose return from
            [[noreturn]] function.

            * g++.dg/cpp1y/pr126354.C: New test.
            * g++.dg/cpp26/pr126354.C: New test.

    Reviewed-by: Jason Merrill <[email protected]>