Re: [PATCH] libstdc++: Optimize operator+(string/char*, string/char*) equally

[Jonathan Wakely <jwakely@redhat.com>]

On Wed, 24 Aug 2022 at 07:18, Will Hawkins <hawkinsw@obs.cr> wrote:
>
> On Tue, Aug 23, 2022 at 12:33 PM Jonathan Wakely <jwakely@redhat.com> wrote:
> >
> > On Mon, 22 Aug 2022 at 19:15, Will Hawkins wrote:
> > >
> > > Until now operator+(char*, string) and operator+(string, char*) had
> > > different performance characteristics. The former required a single
> > > memory allocation and the latter required two. This patch makes the
> > > performance equal.
> >
> > If you don't have a GCC copyright assignment on file with the FSF then
> > please follow the procedure described at https://gcc.gnu.org/dco.html
>
> Thank you.
>
> >
> >
> > > libstdc++-v3/ChangeLog:
> > >         * libstdc++-v3/include/bits/basic_string.h (operator+(string, char*)):
> > >         Remove naive implementation.
> > >         * libstdc++-v3/include/bits/basic_string.tcc (operator+(string, char*)):
> > >         Add single-allocation implementation.
> > > ---
> > >  libstdc++-v3/include/bits/basic_string.h   |  7 +------
> > >  libstdc++-v3/include/bits/basic_string.tcc | 21 +++++++++++++++++++++
> > >  2 files changed, 22 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
> > > index b04fba95678..bc048fc0689 100644
> > > --- a/libstdc++-v3/include/bits/basic_string.h
> > > +++ b/libstdc++-v3/include/bits/basic_string.h
> > > @@ -3523,12 +3523,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
> > >      _GLIBCXX20_CONSTEXPR
> > >      inline basic_string<_CharT, _Traits, _Alloc>
> >
> > Please remove the 'inline' specifier here, since you're moving the
> > definition into the non-inline .tcc file.
> >
> > There's a separate discussion to be had about whether these operator+
> > overloads *should* be inline. But for the purposes of this change, we
> > want these two operator+ overloads to be consistent, and so they
> > should both be non-inline.
>
> Thank you for the feedback. I sent out a v2 of the patch. Again, I
> hope that I followed the proper procedure by having my mailer put the
> patch in reply to my previous message.

It looks like the patch got attached in this thread, not the [PATCH v2] thread:
https://gcc.gnu.org/pipermail/gcc-patches/2022-August/600176.html
Presumably it was meant as a reply to:
https://gcc.gnu.org/pipermail/gcc-patches/2022-August/600175.html

It's more conventional to put the patch in the same email, not as a
separate reply, which would avoid that problem.

You can use git scissors to separate the patch submission from the
preceding discussion and comments, see
https://git-scm.com/docs/git-mailinfo#Documentation/git-mailinfo.txt---scissors

For example, see my patches like the one at
https://gcc.gnu.org/pipermail/gcc-patches/2022-August/600109.html
where the "informational" part comes first, describing where it was
tested, then the patch (and its commit msg) come after the -- >8 --
scissors.

If you use git send-email to send mails, you can use
--in-reply-to=$MessageId to make the email a reply to the specified
$MessageId from a previous mail in the thread.

Anyway, the v2 patch looks fine and I'll apply it to trunk after
testing - thanks!