[Bug c++/123737] [15 Regression] GCC produces incorrect output when overloading operator, comma operator since r15-7089

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123737

--- Comment #13 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-15 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:c8637cd2eea50953208a12a5c7a638b92357612a

commit r15-10887-gc8637cd2eea50953208a12a5c7a638b92357612a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Jan 24 10:38:17 2026 +0100

    c++: Fix wrong-code with overloaded comma and CPP_EMBED [PR123737]

    In cp_parser_expression for comma operator I've used a short path
    where instead of calling build_x_compound_expr #embed number times
    it is called just 3 times, for the CPP_NUMBER added by the preprocessor
    at the start, last byte from CPP_EMBED and then CPP_NUMBER added by
    libcpp at the end, enough to make sure -Wunused-value reports something,
    but not bothering users with millions of -Wunused-value warnings
    and spending too much compile time on it when they use a very large #embed.

    As the following testcases show, that is ok for C or for C++ if the
    expression before it is known not to have OVERLOAD_TYPE_P (common case
    is INTEGER_TYPE I guess), but doesn't work well in case one uses overloaded
    comma operator.  In that case we just have to call build_x_compound_expr
    the right number of times, even if it is a lot.

    I think I don't need to test for !expression, because the preprocessor
    should guarantee that CPP_EMBED is preceded by CPP_NUMBER CPP_COMMA
    tokens.

    2026-01-24  Jakub Jelinek  <jakub@redhat.com>

            PR c++/123737
            * parser.cc (cp_parser_expression): Don't handle CPP_EMBED just
            as the last byte in it if expression has or might have overloaded
            type.  In that case call build_x_compound_expr for each byte
            in CPP_EMBED separately.

            * g++.dg/cpp/embed-28.C: New test.
            * g++.dg/parse/comma3.C: New test.

    (cherry picked from commit e2f626b37ef62fcab8667b2a67318c27a8f2a6ca)