Re: [PATCH] minor optimization bug in basic_string move assignment

[Jonathan Wakely <jwakely.gcc@gmail.com>]

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On Sat, 4 Feb 2023, 13:12 François Dumont via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> On 03/02/23 15:50, Jonathan Wakely wrote:
> > On Wed, 25 Jan 2023 at 18:38, François Dumont <frs.dumont@gmail.com>
> wrote:
> >> Let's submit a proper patch proposal then.
> >>
> >> The occasion for me to ask if there is any reason for cow string not
> >> being C++11 allocator compliant ? Just lack of interest ?
> > Mostly lack of interest, but also I don't really want to "encourage"
> > the use of the old string by investing lots of maintenance effort into
> > it. If you want new features like C++11 Allocators and
> > resize_and_overwrite etc then you should use the new type.
> >
> > I don't remember if there were any actual blockers that made it
> > difficult to support stateful allocators in the COW string. I might
> > have written something about it in mails to the list when I was adding
> > the SSO string, but I don't remember now.
>
> Ok, thanks for feedback. I won't bother then.
>
> >
> > Anyway, for this patch ...
> >
> >> I wanted to consider it to get rid of the __gnu_debug::_Safe_container
> >> _IsCxx11AllocatorAware template parameter.
> >>
> >>       libstdc++: Optimize basic_string move assignment
> >>
> >>       Since resolution of Issue 2593 [1] we can consider that equal
> >> allocators
> >>       before the propagate-on-move-assignment operations will still be
> equal
> >>       afterward.
> >>
> >>       So we can extend the optimization of transfering the storage of
> the
> >> move-to
> >>       instance to the move-from one that is currently limited to always
> equal
> >>       allocators.
> >>
> >>       [1] https://cplusplus.github.io/LWG/issue2593
> >>
> >>       libstdc++-v3/ChangeLog:
> >>
> >>               * include/bits/basic_string.h (operator=(basic_string&&)):
> >> Transfer move-to
> >>               storage to the move-from instance when allocators are
> equal.
> >>               *
> >> testsuite/21_strings/basic_string/allocator/char/move_assign.cc
> (test04):
> >>               New test case.
> >>
> >> Tested under linux x86_64, ok to commit ?
> > OK for trunk, thanks!
> >
> > +Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
>
> Should I have added this to the commit ?
>
> If so sorry, I haven't.
>


No problem!

I think it would be a good habit for us to all start doing that (copying
the glibc project), to thank people who take the time to do a review. I
don't really mind if my name gets recorded as reviewer, but I'm going to
try to remember to add Reviewed-by: when I review something. And that might
encourage others to do the same, and to do more reviewing :-)



>