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Subject: [Bug c++/86369] constexpr const char* comparison fails
Date: Thu, 05 Aug 2021 18:09:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D86369

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Another possibility would be to detect it in cxx_eval_binary_expression bef=
ore
calling fold_binary_loc and punt.

But, the constant evaluation actually doesn't track whether it is the same =
or
different evaluation of the same string literal, so not optimizing it would=
 on
the other side mean we'd reject valid code.  Consider

constexpr auto name3(const char *p) { return p; }

int main() {
    constexpr auto p1 =3D "test3";
    constexpr auto p2 =3D "test4";
    constexpr auto b1 =3D (name3(p1) =3D=3D name3(p1)); // should be true
    constexpr auto b2 =3D (name3(p1) =3D=3D name3(p2)); // should be false
}

Note, latest clang++ seems to accept b1 in both #c0 and #c6 testcases and
reject b2 in both.=