[PATCH] libstdc++: Skip atomic instructions in _Sp_counted_base::_M_release when both counts are 1

[Jonathan Wakely]

On Wed, 8 Dec 2021 at 19:17, Rainer Orth wrote:
>
> Hi Jonathan,
>
> > I've pushed this change to trunk now (it was posted and reviewed in
> > stage 1, I just didn't get around to pushing it until now).
> >
> > The final version of the patch is attached to this mail.
>
> unfortunately, it breaks Solaris/SPARC bootstrap:
>
> In file included from /var/gcc/regression/master/11.4-gcc-gas/build/sparc-sun-solaris2.11/sparcv9/libstdc++-v3/include/bits/shared_ptr.h:53,
>                  from /var/gcc/regression/master/11.4-gcc-gas/build/sparc-sun-solaris2.11/sparcv9/libstdc++-v3/include/memory:77,
>                  from /vol/gcc/src/hg/master/local/libstdc++-v3/include/precompiled/stdc++.h:82:
> /var/gcc/regression/master/11.4-gcc-gas/build/sparc-sun-solaris2.11/sparcv9/libstdc++-v3/include/bits/shared_ptr_base.h: In member function 'void std::_Sp_counted_base<_Lp>::_M_release() [with __gnu_cxx::_Lock_policy _Lp = __gnu_cxx::_S_atomic]':
> /var/gcc/regression/master/11.4-gcc-gas/build/sparc-sun-solaris2.11/sparcv9/libstdc++-v3/include/bits/shared_ptr_base.h:329:26: error: right operand of shift expression '(1 << 64)' is greater than or equal to the precision 64 of the left operand [-fpermissive]
>   329 |             = 1LL + (1LL << (__CHAR_BIT__ * sizeof(_Atomic_word)));
>       |                     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> make[9]: *** [Makefile:1875: sparc-sun-solaris2.11/bits/stdc++.h.gch/O2ggnu++0x.gch] Error 1
>
> For 64-bit SPARC, _Atomic_word is long.

Ah yes, so we need to disable this optimization. Patch coming up ...