220 7281 article Path: news.gmane.org!not-for-mail From: "Billy O'Neal" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Predynamic Storage Duration Date: Sun, 13 Oct 2013 23:50:18 -0700 Lines: 405 Approved: news@gmane.org Message-ID: References: <6fabf6ab-eb9b-42a1-b4a4-deacb2d30ba1@isocpp.org> <8b3bff2b-d0ce-4644-b753-deba2dea954a@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=089e01634ec2f1d81a04e8ade3c7 X-Trace: ger.gmane.org 1381733454 25651 80.91.229.3 (14 Oct 2013 06:50:54 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 14 Oct 2013 06:50:54 +0000 (UTC) To: std-proposals Original-X-From: std-proposals+bncBDKLBLVE6ADBBUVI52JAKGQEPRDS55Y@isocpp.org Mon Oct 14 08:51:00 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vb0-f71.google.com ([209.85.212.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VVbzX-00046z-NB for gclcip-std-proposals@m.gmane.org; Mon, 14 Oct 2013 08:50:59 +0200 Original-Received: by mail-vb0-f71.google.com with SMTP id g17sf13120299vbg.10 for ; Sun, 13 Oct 2013 23:50:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=AQKAHmC6ow4MJlMEbFrI/YmchnGMkVMTs9VSQ8EGuhY=; b=DHnEUJY+lcMupmQo8VDMEmAZylDuPx6h5HxxGDTGB9SZa2XYMf92iBjjW4XBV5Mp++ FxQxKYGoBl+uwiIAw5LqoveytTnvomUBpLOzMzIibeYK/uLjMZZgSRkR9faAQYW36a0H oGdieCIRxj1tviQ5R1/SPBIRNSPmC0xS6u8bSGZBzO76wO3a6YCkMfny+zO57xsHZgLQ SxmYUsX795RM0seG6d0jTKfuPjAIzt6yyWpCOZ+sJFHJ0G/5yfR9N04007kSsBnDzaMB vMqocRuhYeuZc6G0PgBZfGGOJ1vtr0sQRaevyyqK6xFhQa3SKtsllWg2HjG28nPEQxx+ 9ZWA== X-Received: by 10.236.94.39 with SMTP id m27mr154388yhf.54.1381733458919; Sun, 13 Oct 2013 23:50:58 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.131.138 with SMTP id om10ls658732obb.29.gmail; Sun, 13 Oct 2013 23:50:58 -0700 (PDT) X-Received: by 10.182.237.75 with SMTP id va11mr27193162obc.5.1381733458300; Sun, 13 Oct 2013 23:50:58 -0700 (PDT) Original-Received: from mail-oa0-x235.google.com (mail-oa0-x235.google.com [2607:f8b0:4003:c02::235]) by mx.google.com with ESMTPS id h5si31733710oed.14.1969.12.31.16.00.00 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 13 Oct 2013 23:50:58 -0700 (PDT) Received-SPF: pass (google.com: domain of billy.oneal@gmail.com designates 2607:f8b0:4003:c02::235 as permitted sender) client-ip=2607:f8b0:4003:c02::235; Original-Received: by mail-oa0-f53.google.com with SMTP id i7so4211752oag.40 for ; Sun, 13 Oct 2013 23:50:58 -0700 (PDT) X-Received: by 10.182.250.163 with SMTP id zd3mr27088866obc.20.1381733458104; Sun, 13 Oct 2013 23:50:58 -0700 (PDT) Original-Received: by 10.182.87.37 with HTTP; Sun, 13 Oct 2013 23:50:18 -0700 (PDT) In-Reply-To: <8b3bff2b-d0ce-4644-b753-deba2dea954a@isocpp.org> X-Original-Sender: billy.oneal@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of billy.oneal@gmail.com designates 2607:f8b0:4003:c02::235 as permitted sender) smtp.mail=billy.oneal@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.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:7281 Archived-At: --089e01634ec2f1d81a04e8ade3c7 Content-Type: text/plain; charset=ISO-8859-1 >The main use case would be enabling the use of strings, vectors and other types that use dynamic storage as parameters, local variables and return types of constexpr functions Ok, I agree that's interesting. But your proposal started out with "I want [code sample] to be as efficient as [code sample]." Billy O'Neal https://github.com/BillyONeal/ http://stackoverflow.com/users/82320/billy-oneal Malware Response Instructor - BleepingComputer.com On Sun, Oct 13, 2013 at 11:47 PM, Andrew Tomazos wrote: > > On Monday, October 14, 2013 6:53:05 AM UTC+2, Billy O'Neal wrote: >> >> I can't think of a real world use case where this would have a >> significant performance impact, and it adds significant complexity >> penalties into the core language. >> > > The main use case would be enabling the use of strings, vectors and other > types that use dynamic storage as parameters, local variables and return > types of constexpr functions. Constexpr functions can be evaluated during > translation from within a constant expression - so enable trading one unit > of compile-time for at least n units of run-time, where n is the number of > times the program is executed, for a net benefit of at least n-1 units of > performance. > > The specific use cases of using strings and vectors in functions are too > numerous to mention. One example would be writing a character encoding > transcoder. Such a function may take a string in the input character > encoding and return a string in the output character encoding and use a > local vector object to hold an intermediate representation: > > constexpr std::string transcode(const std::string& input) > { > std::vector points; > > for (char c : input) > { > ... > if (b) > points.push_back(x); > } > > std::string output; > > for (int x : points) > { > if (...) > output += ...; > } > > return output; > } > > constexpr std::string s = transcode("foo"); > > In the above transcode is called during translation and s is then > constant-initialized. It doesn't take much creativity to think of a whole > host of other uses. > -Andrew. > > > Billy O'Neal >> https://github.com/BillyONeal/ >> http://stackoverflow.com/**users/82320/billy-oneal >> Malware Response Instructor - BleepingComputer.com >> >> >> On Sun, Oct 13, 2013 at 9:25 PM, Andrew Tomazos wrote: >> >>> I want this: >>> >>> std::string s = "foo"; >>> std::vector v = {1,2,3}; >>> >>> to be as efficient as this: >>> >>> char s[] = "foo"; >>> int v[] = {1,2,3}; >>> >>> and I want to write this: >>> >>> constexpr std::vector f(...) >>> { >>> std::vector v; >>> >>> for (...) >>> { >>> ... >>> >>> v.push_back(v); >>> } >>> >>> return v; >>> } >>> >>> Basically, I want std::string, std::vector and similar classes to be >>> literal types. >>> >>> The main reason they cannot currently be literal types is because they >>> need to allocate objects of dynamic storage duration, and the heap isn't >>> available during translation. >>> >>> So here are the proposed changes: >>> >>> - Allow new expressions and delete expressions within constexpr >>> functions (provided the operands are of literal type.) >>> >>> - A new expression evaluated within a constexpr function in >>> constant-context returns a pointer to an object of predynamic storage >>> duration >>> >>> - A delete expression evaluated within a constexpr function in >>> constant-context deletes an object of predynamic storage duration >>> >>> - A delete expression evaluated at run-time deletes an object of either >>> predynamic or dynamic storage duration >>> >>> Essentially, predynamic storage duration starts during translation and >>> can end as late as run-time. >>> >>> During translation when evaluating a new expression within a constexpr >>> function the implementation allocates the object within a memory pool >>> (using whatever internal system it uses to hold variables of literal type) >>> we'll call the preheap. When encountering a delete expression in a >>> constexpr function it deletes the operand from the preheap. Any predynamic >>> objects left over in the preheap after translation has completed are >>> arranged into the program image in a .preheap section. When the program >>> loads the .preheap section is copied into memory and serves as part of the >>> initial state of the run-time heap. >>> >>> constexpr int* f() >>> { >>> int a[] = {1,2,3}; >>> >>> int* b = new int[3]; // predynamic object allocated during >>> translation >>> >>> for (size_t i = 0; i < 3; i++) >>> b[i] = a[i]; >>> >>> return b; >>> } >>> >>> constexpr int* p = f(); // f called duration translation, returns >>> pointer to predynamic object >>> >>> int main() >>> { >>> delete p; // deletes predynamic object at runtime >>> } >>> >>> Feedback/thoughts appreciated. >>> >>> >>> -- >>> >>> --- >>> 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-proposal...@**isocpp.org. >>> To post to this group, send email to std-pr...@isocpp.org. >>> >>> Visit this group at http://groups.google.com/a/**isocpp.org/group/std-** >>> proposals/ . >>> >> >> -- > > --- > 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. > Visit this group at > http://groups.google.com/a/isocpp.org/group/std-proposals/. > -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --089e01634ec2f1d81a04e8ade3c7 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
>The main use case would be enabling the use of st= rings, vectors and other types that use dynamic storage as parameters, loca= l variables and return types of constexpr functions
=A0
Ok, I agree that's interesting. But your proposal started out with &quo= t;I want [code sample] to be as efficient as [code sample]."

B= illy O'Neal
Malware Response Instructor - BleepingComputer.com


On Sun, Oct 13, 2013 at 11:47 PM, Andrew= Tomazos <andrewtomazos@gmail.com> wrote:

On Monday, October 14, 2013 6:53:05 = AM UTC+2, Billy O'Neal wrote:
I can't think of a real world use case where this would have a=20 significant performance impact, and it adds significant complexity=20 penalties into the core language.

The main use = case would be enabling the use of strings, vectors and other types that use= dynamic storage as parameters, local variables and return types of constex= pr functions.=A0 Constexpr functions can be evaluated during translation fr= om within a constant expression - so enable trading one unit of compile-tim= e for at least n units of run-time, where n is the number of times the prog= ram is executed, for a net benefit of at least n-1 units of performance.
The specific use cases of using strings and vectors in functions are to= o numerous to mention.=A0 One example would be writing a character encoding= transcoder.=A0 Such a function may take a string in the input character en= coding and return a string in the output character encoding and use a local= vector object to hold an intermediate representation:

=A0=A0=A0 constexpr std::string transcode(const std::string& input)=
=A0=A0=A0 {
=A0=A0=A0=A0=A0=A0=A0 std::vector<int> points;
=
=A0=A0=A0=A0=A0=A0=A0 for (char c : input)
=A0=A0=A0=A0=A0=A0=A0 {=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ...
=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 if (b)
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 points= ..push_back(x);
=A0=A0=A0=A0=A0=A0=A0 }

=A0=A0=A0=A0=A0=A0=A0 std::string output;
=A0=A0=A0=A0=A0=A0=A0 for (int x : points)
=A0=A0=A0=A0=A0=A0=A0 {<= br>=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (...)
=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0 output +=3D ...;
=A0=A0=A0=A0=A0=A0=A0 }

=A0= =A0=A0=A0=A0=A0=A0 return output;
=A0=A0=A0 }

=A0=A0=A0 constexpr= std::string s =3D transcode("foo");

In the above transcode is called during translation and s is then const= ant-initialized.=A0 It doesn't take much creativity to think of a whole= host of other uses.
=A0=A0 -Andrew.


Billy O&= #39;Neal
Malware Response Instructor - BleepingComputer.com


On Sun, Oct= 13, 2013 at 9:25 PM, Andrew Tomazos <andrew...@gma= il.com> wrote:
I want this:

=A0=A0=A0 std::string s =3D "foo&= quot;;
=A0=A0=A0 std::vector<int> v =3D {1,2,3};

to be as e= fficient as this:

=A0=A0=A0 char s[] =3D "foo";
=A0=A0= =A0 int v[] =3D {1,2,3};

and I want to write this:

=A0=A0=A0 constexpr std::vector<int>= f(...)
=A0=A0=A0 {
=A0=A0=A0=A0=A0=A0=A0 std::vector<int> v;
=A0=A0=A0=A0=A0=A0=A0 for (...)
=A0=A0=A0=A0=A0=A0=A0 {
=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ...

=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 v.push_back(v);
=A0=A0=A0=A0=A0=A0=A0 }

=A0=A0=A0=A0=A0=A0=A0 return v;
=A0=A0=A0 }

Basically, I want= std::string, std::vector and similar classes to be literal types.

T= he main reason they cannot currently be literal types is because they need = to allocate objects of dynamic storage duration, and the heap isn't ava= ilable during translation.

So here are the proposed changes:

- Allow new expressions and de= lete expressions within constexpr functions (provided the operands are of l= iteral type.)

- A new expression evaluated within a constexpr functi= on in constant-context returns a pointer to an object of predynamic storage= duration

- A delete expression evaluated within a constexpr function in constant= -context deletes an object of predynamic storage duration

- A delete= expression evaluated at run-time deletes an object of either predynamic or= dynamic storage duration

Essentially, predynamic storage duration starts during translation and = can end as late as run-time.

During translation when evaluating a ne= w expression within a constexpr function the implementation allocates the o= bject within a memory pool (using whatever internal system it uses to hold = variables of literal type) we'll call the preheap.=A0 When encountering= a delete expression in a constexpr function it deletes the operand from th= e preheap.=A0 Any predynamic objects left over in the preheap after transla= tion has completed are arranged into the program image in a .preheap sectio= n.=A0 When the program loads the .preheap section is copied into memory and= serves as part of the initial state of the run-time heap.

=A0=A0=A0 constexpr int* f()
=A0=A0=A0 {
=A0=A0=A0=A0=A0=A0=A0 in= t a[] =3D {1,2,3};

=A0=A0=A0=A0=A0=A0=A0 int* b =3D new int[3];=A0 /= / predynamic object allocated during translation

=A0=A0=A0=A0=A0=A0= =A0 for (size_t i =3D 0; i < 3; i++)
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 b[i] =3D a[i];

=A0=A0=A0=A0=A0=A0=A0 return b;
=A0=A0=A0=A0 }

=A0=A0=A0=A0 c= onstexpr int* p =3D f(); // f called duration translation, returns pointer = to predynamic object

=A0=A0=A0=A0 int main()
=A0=A0=A0=A0 {
= =A0=A0=A0=A0=A0=A0=A0=A0 delete p; // deletes predynamic object at runtime<= br> =A0=A0=A0=A0 }

Feedback/thoughts appreciated.


--
=A0
---
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposal...@isocpp.org.
To post to this group, send email to std-pr...@isocpp.org.

Visit this group at http://groups.google.com/a/isocpp.= org/group/std-proposals/.

--
=A0
---
You received this message because you are subscribed to the Google Groups &= quot;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.
Visit this group at http://groups.google.com/a/isocpp.org/gro= up/std-proposals/.

--
 
---
You received this message because you are subscribed to the Google Groups &= quot;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.
Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/<= /a>.
--089e01634ec2f1d81a04e8ade3c7-- .