[Bug c++/104243] Optimization requires __sync_synchronize

[marxin at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104243

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
It's related to fact that the following function is pure:

    [[nodiscard]] __attribute__((visibility("default"))) static
__attribute__((pure)) QVersionNumber fromString(const QString &string, int
*suffixIndex = nullptr);

    [[nodiscard]] __attribute__((visibility("default"))) static
__attribute__((pure)) QVersionNumber fromString(QLatin1String string, int
*suffixIndex = nullptr);
    [[nodiscard]] __attribute__((visibility("default"))) static
__attribute__((pure)) QVersionNumber fromString(QStringView string, int
*suffixIndex = nullptr);

and thus we optimize out: qt.ii.037t.fre1

Replaced idx with 0 in all uses of idx.0_1 = idx;
Removing unexecutable edge from if (idx.0_1 == 0)
Removing dead stmt idx.0_1 = idx;