220 40320 article Path: news.gmane.org!.POSTED!not-for-mail From: Ren Industries Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Runtime code generation and self modifying code Date: Thu, 4 Oct 2018 20:57:47 -0400 Lines: 100 Approved: news@gmane.org Message-ID: References: <4489f889-977c-45f2-8a2f-186ee3b06bff@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="000000000000ce3d65057770c21c" X-Trace: blaine.gmane.org 1538700957 1158 195.159.176.226 (5 Oct 2018 00:55:57 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 5 Oct 2018 00:55:57 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDILF3OBTACRBGPO3LOQKGQEQBRF23Y@isocpp.org Fri Oct 05 02:55:53 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it1-f199.google.com ([209.85.166.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1g8EPI-0000Bt-Gf for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id d193-v6sor2934273ioe.130.2018.10.04.17.57.52 for (Google Transport Security); Thu, 04 Oct 2018 17:57:52 -0700 (PDT) Received-SPF: pass (google.com: domain of renindustries@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a6b:610a:: with SMTP id v10-v6mr6611035iob.107.1538701071889; Thu, 04 Oct 2018 17:57:51 -0700 (PDT) In-Reply-To: <4489f889-977c-45f2-8a2f-186ee3b06bff@isocpp.org> X-Original-Sender: RenIndustries@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=FDeyJwpY; spf=pass (google.com: domain of renindustries@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=renindustries@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:40320 Archived-At: --000000000000ce3d65057770c21c Content-Type: text/plain; charset="UTF-8" Couldn't a compiler just output that code for this idiom? Sounds like a QOI issue. On Thu, Oct 4, 2018 at 8:35 PM Matthew Fioravante wrote: > One big area where dynamic languages are way ahead of C++ is runtime > dynamic code generation or self modifying code. > > > One tiny example is singleton initialization. The only safe way in C++ to > do non-constexpr singletons is by lazy init. > > The problem with lazy init is that you have to pay for a branch on every > access, and that usually involves an atomic check. > > What if you instead you atomically overwrote the check with NOPS. Then the > branch is gone and accessing the object is as efficient as if it weren't > lazy. > > Has anyone considered writing proposals for improving runtime code gen > with C++? > > -- > You received this message because you are subscribed to the Google Groups > "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to std-proposals+unsubscribe@isocpp.org. > To post to this group, send email to std-proposals@isocpp.org. > To view this discussion on the web visit > https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/4489f889-977c-45f2-8a2f-186ee3b06bff%40isocpp.org > > . > -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAMD6iD_1Xqqa7Qjv35FaCH1Q39Jitr8Okwds-_2i0wWxz6EEYA%40mail.gmail.com. --000000000000ce3d65057770c21c Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Couldn't a compiler just output that code for this idi= om?
Sounds like a QOI issue.

=
On Thu, Oct 4, 2018 at 8:35 PM Matthew Fioravante <fmatthew5876@gmail.com> wrote:=
One big area= where dynamic languages are way ahead of C++ is runtime dynamic code gener= ation or self modifying code.


O= ne tiny example is singleton initialization. The only safe way in C++ to do= non-constexpr singletons is by lazy init.

Th= e problem with lazy init is that you have to pay for a branch on every acce= ss, and that usually involves an atomic check.

Wha= t if you instead you atomically overwrote the check with NOPS. Then the bra= nch is gone and accessing the object is as efficient as if it weren't l= azy.

Has anyone considered writing proposals f= or improving runtime code gen with C++?

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