From: "François Dumont" <frs.dumont@gmail.com>
To: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: libstdc++ <libstdc++@gcc.gnu.org>
Subject: Re: [committed] libstdc++: Reduce header dependencies for C++20 std::erase [PR92546]
Date: Thu, 7 Oct 2021 08:35:30 +0200 [thread overview]
Message-ID: <237efbd9-abd4-47e9-0af9-dace431d5da7@gmail.com> (raw)
In-Reply-To: <CAH6eHdR8YdHKR=esJ4Os6BudiqMdxmy9vREFFdqrx4VR96k+Fg@mail.gmail.com>
On 02/10/21 2:47 pm, Jonathan Wakely wrote:
>
>
> On Sat, 2 Oct 2021, 13:02 François Dumont via Libstdc++,
> <libstdc++@gcc.gnu.org <mailto:libstdc%2B%2B@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.
It is in a method called '__erases_node_if', I'm not aware of any
node-based container providing random access iterators.
Moreover I just noticed that if it was really doing anything then you
would be missing the std::__niter_wrap in the __cont.erase(__iter), it
just wouldn't compile.
>
> 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.
Yes, that would be better indeed.
But doing it this way you still have the overhead of the _Safe_iterator
addition to the list of the safe container iterators, so a mutex
lock/unlock.
I'll try to find out how to get a normal iterator from a safe container
even if in this case we will have to support operations on safe
container with normal iterators.
next prev parent reply other threads:[~2021-10-07 6:35 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 19:38 Jonathan Wakely
2021-10-02 12:01 ` François Dumont
2021-10-02 12:47 ` Jonathan Wakely
2021-10-07 6:35 ` François Dumont [this message]
2021-10-07 6:51 ` Jonathan Wakely
2021-10-07 14:02 ` Jonathan Wakely
2021-10-07 17:05 ` [committed] libstdc++: Avoid debug checks in uniform container erasure functions Jonathan Wakely
2021-10-07 17:06 ` [committed] libstdc++: Reduce header dependencies for C++20 std::erase [PR92546] François Dumont
2021-10-07 17:16 ` Jonathan Wakely
2021-10-07 17:34 ` François Dumont
2021-10-07 18:34 ` Jonathan Wakely
2021-10-07 19:51 ` François Dumont
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=237efbd9-abd4-47e9-0af9-dace431d5da7@gmail.com \
--to=frs.dumont@gmail.com \
--cc=jwakely.gcc@gmail.com \
--cc=libstdc++@gcc.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).