220 39 article Path: news.gmane.org!not-for-mail From: stackmachine@hotmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allowing constexpr char[]'s in asm directives Date: Sun, 11 Nov 2012 07:02:04 -0800 (PST) Lines: 100 Approved: news@gmane.org Message-ID: References: <27482d3f-117d-4913-b1ff-feb6267760f3@isocpp.org> <509DFF12.9060206@gmx.net> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_324_26262145.1352646124819" X-Trace: ger.gmane.org 1352646127 20319 80.91.229.3 (11 Nov 2012 15:02:07 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 11 Nov 2012 15:02:07 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDC7BQ4GSIMRB3P372CAKGQEX5CLIUA@isocpp.org Sun Nov 11 16:02:18 2012 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yh0-f70.google.com ([209.85.213.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1TXZ3A-0007SC-2t for gclcip-std-proposals@m.gmane.org; Sun, 11 Nov 2012 16:02:16 +0100 Original-Received: by mail-yh0-f70.google.com with SMTP id o21sf9343894yho.9 for ; Sun, 11 Nov 2012 07:02:06 -0800 (PST) Original-Received: by 10.236.193.73 with SMTP id j49mr11878126yhn.7.1352646126061; Sun, 11 Nov 2012 07:02:06 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.236.114.196 with SMTP id c44ls8230643yhh.7.gmail; Sun, 11 Nov 2012 07:02:05 -0800 (PST) Original-Received: by 10.236.149.66 with SMTP id w42mr2139426yhj.18.1352646125716; Sun, 11 Nov 2012 07:02:05 -0800 (PST) In-Reply-To: <509DFF12.9060206@gmx.net> X-Original-Sender: stackmachine@hotmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: 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:39 Archived-At: ------=_Part_324_26262145.1352646124819 Content-Type: text/plain; charset=ISO-8859-1 Am Samstag, 10. November 2012 08:16:19 UTC+1 schrieb Jens Maurer: > > On 11/10/2012 02:15 AM, stackm...@hotmail.com wrote: > > Simple feature: Allow the use of compiletime constant strings in asm > directives. That would allow generating asm through template-meta programs. > Wouldn't that be damn awesome? > > Could you provide an example program that makes use of such a > feature in a non-trivial way, including the generation of > the compile-time constant strings? In which way would the > portability of that program be improved if the standard > would prescribe the feature you're proposing? > The program would not neccessarily be more portable but it would allow (for example) simple abstractions around common patterns, such as loops, conditions, or function calls. Here's a simple example of how this could be used: typedef function print_int; // assuming that string literals could be used as template parameters in the future typedef for_from_to<1, 10, call> print_1_to_10; asm(generate_asm::value::c_str); ::value might be some compiletime string type, which itself holds a constexpr char[] ::c_str. Now I do admit that this example might not be the best, but it demonstrates one important aspect of this feature: The programmer does not have to deal with details, such as calling conventions, as this is handled by the library that generates the code. > The current standard doesn't say a lot about "asm" (see section 7.4), > except that its argument must be a string-literal. And even then, > the entire asm is conditionally-supported, meaning an implementation > can simply refuse an "asm" with an error message (and not implement it). > Instead of only allowing string literals, I propose to allow constant string expressions. This would only require a change to the grammar AFAIK. (?) -- ------=_Part_324_26262145.1352646124819 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

Am Samstag, 10. November 2012 08:16:19 UTC+1 schrieb Jens Maurer:On 11/10/2012 02:15 AM, s= tackm...@hotmail.com wrote:
> Simple feature: Allow the use of compiletime constant strings in a= sm directives. That would allow generating asm through template-meta progra= ms. Wouldn't that be damn awesome?

Could you provide an example program that makes use of such a
feature in a non-trivial way, including the generation of
the compile-time constant strings?  In which way would the
portability of that program be improved if the standard
would prescribe the feature you're proposing?
The program would not neccessarily be more portable b= ut it would allow (for example) simple abstractions around common patterns,= such as loops, conditions, or function calls.
Here's a simple example o= f how this could be used:

typedef function<stdcall, "print_int"&g= t; print_int; // assuming that string literals could be used as template pa= rameters in the future
typedef for_from_to<1, 10, call<print_int&g= t;> print_1_to_10;

asm(generate_asm<x86_64, print_1_to_10>:= :value::c_str);

::value might be some compiletime string type, which= itself holds a constexpr char[] ::c_str.
Now I do admit that this examp= le might not be the best, but it demonstrates one important aspect of this = feature: The programmer does not have to deal with details, such as calling= conventions, as this is handled by the library that generates the code.
 
Th= e current standard doesn't say a lot about "asm" (see section 7.4),
except that its argument must be a string-literal.  And even then,
the entire asm is conditionally-supported, meaning an implementation
can simply refuse an "asm" with an error message (and not implement it)= ..
Instead of only allowing string literals, I propose = to allow constant string expressions. This would only require a change to t= he grammar AFAIK. (?)

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