220 41235 article Path: news.gmane.org!.POSTED!not-for-mail From: Tom Honermann Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Modules and preambule, just why? Date: Fri, 7 Dec 2018 10:48:38 -0500 Lines: 73 Approved: news@gmane.org Message-ID: References: <16989401-2f0d-4200-997e-0ac60b47bec3@isocpp.org> <08290107-c63b-3ef6-09d4-16c7b6c495ab@honermann.net> <0727d34e-0bad-3689-e315-2136bb359e65@honermann.net> <41ef0549-4ff9-4d0d-b033-5eb30055490c@isocpp.org> <36e9388e-9b8d-4c93-9a0a-bedfb00c135f@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1544197596 10070 195.159.176.226 (7 Dec 2018 15:46:36 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 7 Dec 2018 15:46:36 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 Cc: ville.voutilainen@gmail.com To: std-proposals@isocpp.org, Victor Dyachenko Original-X-From: std-proposals+bncBDBNXSHG6UDBBWFMVLQAKGQEAL46TFY@isocpp.org Fri Dec 07 16:46:31 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it1-f198.google.com ([209.85.166.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gVIKl-0002XN-Gn for gclcip-std-proposals@m.gmane.org; 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[108.166.43.83]) by mx.google.com with ESMTPS id i12si1822506iol.27.2018.12.07.07.48.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 07 Dec 2018 07:48:40 -0800 (PST) Received-SPF: pass (google.com: domain of tom@honermann.net designates 108.166.43.83 as permitted sender) client-ip=108.166.43.83; Original-Received: from smtp19.relay.ord1c.emailsrvr.com (localhost [127.0.0.1]) by smtp19.relay.ord1c.emailsrvr.com (SMTP Server) with ESMTP id CB451A05A3; Fri, 7 Dec 2018 10:48:39 -0500 (EST) X-Auth-ID: tom@honermann.net Original-Received: by smtp19.relay.ord1c.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 7225CA0595; Fri, 7 Dec 2018 10:48:39 -0500 (EST) X-Sender-Id: tom@honermann.net Original-Received: from [192.168.1.19] (pool-71-176-235-158.rcmdva.fios.verizon.net [71.176.235.158]) (using TLSv1.2 with cipher AES128-SHA) by 0.0.0.0:587 (trex/5.7.12); Fri, 07 Dec 2018 10:48:39 -0500 In-Reply-To: <36e9388e-9b8d-4c93-9a0a-bedfb00c135f@isocpp.org> Content-Language: en-US X-Original-Sender: tom@honermann.net X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@honermann.net header.s=20180930-2j89z3ji header.b=LMS9AOys; spf=pass (google.com: domain of tom@honermann.net designates 108.166.43.83 as permitted sender) smtp.mailfrom=tom@honermann.net; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=honermann.net 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:41235 Archived-At: On 12/7/18 12:57 AM, Victor Dyachenko wrote: > IIRC initially modules were based on some sort of high-level C++ AST=20 > representation - XPR=20 > (https://parasol.tamu.edu/pivot/publications/user-guide.pdf). I'm=20 > talking about Gaby's/VC++ implementation. Do they use different=20 > approach now? My understanding is that Microsoft is (still) using an internal fork of=20 IPR (https://github.com/GabrielDosReis/ipr). > A there any people here aware of gcc/clang approach? Clang uses its own AST serialization format.=C2=A0 It is the same format=20 Clang uses for pre-compiled headers, .ast files, and traditional Clang=20 modules.=C2=A0 These files are Clang specific and not historically compatib= le=20 across Clang versions. Gcc is also using its own AST serialization format that reflects gcc's=20 internal AST.=C2=A0 Nathan Sidwell discusses this in some of his talks.=C2= =A0 You=20 might want to watch his talk from this year's GNU Tools Cauldron=20 (https://www.youtube.com/watch?v=3D5CadIjPRZpM).=C2=A0 He talks about AST= =20 serialization around the 20 minute mark. > And if XPR is enough to represent modules interface files (is it?),=20 > can't it be standardized at least in theory? IPR has limitations.=C2=A0 For example, it does not store full source=20 information nor preprocessor information (no column or macro expansion=20 information).=C2=A0 This means consumers can't accurately map imported=20 constructs back to source code (for example, in diagnostics). In practice, I don't think something can be standardized here, nor do I=20 think it would be beneficial.=C2=A0 There are competing requirements for ho= w=20 much data to store (different compilers/tools need different=20 information).=C2=A0 A goal of modules is to improve compile times and a=20 common format would impose overhead relative to what can be accomplished=20 with a highly optimized compiler/tool specific format.=C2=A0 Harder questio= ns=20 involve implementation defined things.=C2=A0 How would compiler intrinsics= =20 and language extensions be handled?=C2=A0 How would implementation defined= =20 behavior in general be handled?=C2=A0 (The standard has many cases where=20 implementation defined behavior can impact the AST).=C2=A0 The committee ha= s=20 discussed this a number of times and my impression is that there is no=20 consensus for a standard format (though the committee has not actually=20 polled this). I think a more interesting question is, what would a standard format=20 enable you to do that you wouldn't be able to otherwise? Can we enable=20 those goals in another way?=C2=A0 For example, would implementation specifi= c=20 tools (potentially defacto industry standards like c++filt) that expose=20 information from module artifacts, potentially in some standard format,=20 be helpful? Tom. --=20 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 e= mail 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/ea2a691d-f8bb-2d5c-86ce-9515b9f1350f%40honermann= ..net. .