[PATCH v2] libstdc++: restore old _M_create behavior [PR127228]

[Jonathan Wakely]

On Tue, 13 Oct 2026 at 18:22, Jonathan Wakely <jwakely@redhat.com> wrote:
>
>
>
> On Tue, 13 Oct 2026 at 17:04, Nathan Myers <ncm@cantrip.org> wrote:
>>
>> Changes in v2:
>>  - Remove helper function, use -fnoaccess-control and call
>>   _M_create directly instead.
>>  - Build test with -fno-ipa-* flags.
>>  - Add check for capacity 2.
>>  - Scrub opinion about _M_create's semantics.
>
>
> OK, thanks.

The new test fails for -D_GLIBCXX_USE_CXX11_ABI=0

/home/test/src/gcc/libstdc++-v3/testsuite/21_strings/basic_string/127228.cc:17:
error: 'std::string' {aka 'class std::basic_string<char>'} has no
member named '_M_create'; did you mean '_M_mutate'?

It needs { dg-require-effective-target cxx11_abi } so that it's
UNSUPPORTED for the old COW string, instead of FAIL.