Re: [PATCH] libstdc++: use new built-in trait __is_reference

[Ken Matsui <kmatsui@cs.washington.edu>]

> Does it actually make compilation faster though?
>
> Has it been measured?

In my understanding, what I have implemented so far is so simple that
it does not affect the speed. These traits are what Partick kindly
recommended to get started. As explained on the GSoC page, some traits
might involve expensive instantiation of multiple class templates. So
IMHO, implementing built-in traits for those traits can make
compilation cheaper.

I have not measured it, but Patrick might have done?

On Mon, Mar 20, 2023 at 2:14 AM Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>
> On Mon, 20 Mar 2023 at 08:08, Xi Ruoyao via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > On Mon, 2023-03-20 at 01:03 -0700, Ken Matsui wrote:
> > > Oops, I assumed those were my email... Thank you for your heads up and
> > > your comments!
> > >
> > > > Bad ChangeLog format.  You should have a tab (not 4 or 8 spaces, nor
> > > > nothing) to indent the ChangeLog content.
> > >
> > > Do you mean like the following?
> > >
> > > ```
> > > libstdc++-v3/ChangeLog:
> > >
> > > [TAB]* include/std/type_traits (is_reference): Use __is_reference
> > > built-in
> > > trait.
> > > ```
> >
> > Yep.
> >
> > > > Is there any benefit to use a builtin, instead of the existing
> > > > implementation?  I can see no but maybe I'm stupid.
> > >
> > > My patches are based on the GSoC project "C++: Implement compiler
> > > built-in traits for the standard library traits". These built-in
> > > traits basically make the compilation faster.
> > >
> > > https://gcc.gnu.org/wiki/SummerOfCode
> >
> > Ok, to me making compilation faster is a valid reason.
>
> Does it actually make compilation faster though?
>
> Has it been measured?
>
> > > > The patch fails to apply.  It seems because your mail client inserted an
> > > > additional newline before "b/".  Try to use git-send-email or configure
> > > > the mail client properly.
> > >
> > > Let me try to use git-send-email instead. I stupidly don't understand
> > > how to use them, so I was making my patches manually...
> >
> > Or adjust the mail client correctly.  You can send the patch to yourself
> > first and see if it's not "mangled" by the mail client when you debug
> > such an issue...
> >
> > But when you finally end up sending 10 patches in a series you'll find
> > git send-email much easier :).
>
> Figuring out how to generate proper patches is an important part of
> contributing to GCC, so part of any GSoC project.