[Bug libstdc++/77582] Improve std::string::clear performace

[xiyou.wangcong at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77582

--- Comment #3 from Cong Wang <xiyou.wangcong at gmail dot com> ---
Hi, Andrew

I just posted it:
https://gcc.gnu.org/ml/libstdc++/2016-09/msg00051.html

Please review.

I caught this when using Google protobuf on Fedora 21, _M_mutate() is shown in
perf top profile, inlined into clear(). AFAIK, only !_GLIBCXX_USE_CXX11_ABI
impl uses _M_mutate().

Thanks.