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

[redi at gcc dot gnu.org]

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

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Fri Sep 23 17:25:34 2016
New Revision: 240447

URL: https://gcc.gnu.org/viewcvs?rev=240447&root=gcc&view=rev
Log:
Avoid reallocation for basic_string::clear()

        PR libstdc++/56166
        PR libstdc++/77582
        * include/bits/basic_string.h (basic_string::clear()): Drop reference
        and use empty rep.
        * include/ext/rc_string_base.h (__rc_string_base::_M_clear()):
        Likewise.
        * testsuite/21_strings/basic_string/56166.cc: New.
        * testsuite/ext/vstring/modifiers/clear/56166.cc: New.

Added:
    trunk/libstdc++-v3/testsuite/21_strings/basic_string/56166.cc
    trunk/libstdc++-v3/testsuite/ext/vstring/modifiers/clear/
    trunk/libstdc++-v3/testsuite/ext/vstring/modifiers/clear/56166.cc
Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/bits/basic_string.h
    trunk/libstdc++-v3/include/ext/rc_string_base.h