Thank you so much for taking the benchmark! This is a great improvement
than I thought.

In GCC contributions, do I need to benchmark (and report) every built-in
trait I implement?

On Mon, Mar 20, 2023 at 8:24 AM Patrick Palka <ppalka@redhat.com> wrote:

> On Mon, Mar 20, 2023 at 5:56 AM Ken Matsui <kmatsui@cs.washington.edu>
> wrote:
> >
> > > 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?
>
> Although the native implementation of using two partial
> specializations is very efficient, I'd suspect using a built-in would
> be even better because it'd avoid the work of having to figure out
> which of the two partial specializations to instantiate.
>
> I contrived the attached benchmark to measure this, which instantiates
> ~160k specializations of is_reference_v (it was simpler to write a
> benchmark for the variable template version). On my machine gcc trunk
> (release build) as well as Clang 15 use between 10-15% less
> time/memory with -DUSE_BUILTIN than without for this benchmark, so
> this suggests the built-in improves compile time/memory usage for this
> trait by at least 10-15%.  For more complicated traits the improvement
> should be even better.
>
> >
> > 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.
> >
>