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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Sat, 2 Oct 2021 13:47:55 +0100
Message-ID: <CAH6eHdR8YdHKR=esJ4Os6BudiqMdxmy9vREFFdqrx4VR96k+Fg@mail.gmail.com>
Subject: Re: [committed] libstdc++: Reduce header dependencies for C++20
 std::erase [PR92546]
To: =?UTF-8?Q?Fran=C3=A7ois_Dumont?= <frs.dumont@gmail.com>
Cc: "libstdc++" <libstdc++@gcc.gnu.org>
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On Sat, 2 Oct 2021, 13:02 Fran=C3=A7ois Dumont via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> On 01/10/21 9:38 pm, Jonathan Wakely via Libstdc++ wrote:
> > This reduces the preprocessed size of <deque>, <string> and <vector> by
> > not including <bits/stl_algo.h> for std::remove and std::remove_if.
> >
> > Also unwrap iterators using __niter_base, to avoid redundant debug mode
> > checks.
>
> I don't know if you noticed but the __niter_base is a no-op here.
>

Oh, I didn't notice.


> __niter_base unwrap only random access iterators because it is the only
> category for which we know that we have been able to confirm validity or
> not.
>

But these are all random access. I must be missing something.


> We would need to introduce another function to do this or specialize in
> some way erase_if for debug containers. I'll try to find a solution.
>

OK, thanks. Maybe we can just leave the checking there. I wanted to avoid
the overhead because we know that the iterator range is valid. Any checks
done on each increment and equality comparison are wasteful, as they will
never fail.




>
> >
> >       PR libstdc++/92546
> >       * include/bits/erase_if.h (__erase_nodes_if): Use __niter_base to
> >       unwrap debug iterators.
> >       * include/bits/refwrap.h: Do not error if included in C++03.
> >       * include/bits/stl_algo.h (__remove_if): Move to ...
> >       * include/bits/stl_algobase.h (__remove_if): ... here.
> >       * include/std/deque (erase, erase_if): Use __remove_if instead of
> >       remove and remove_if.
> >       * include/std/string (erase, erase_if): Likewise.
> >       * include/std/vector (erase, erase_if): Likewise.
> >
> > Tested powerpc64le-linux. Committed to trunk.
> >
> > ff7793bea46
> > 34e9407b3b4
> > b7e8fb5e482
> > 6ccffeb56b9
> > e79bde6ada4
> > e5c093e515c
> > 20751fad19e
> > 9b790acc220
> > e3869a48fc2
> > 44967af830a
> > dc1b29508d7
> > 59ffa3e3dba
> > d71476c9df9
> > a09bb4a852f
> > cfb582f6279
> > c46ecb0112e
> > fb4d55ef61c
> > 10b6d89badd
> > ce709ad3dc0
> > d335d73889d
> > 681707ec28d
> > 741c7350c08
>
>
>