Re: Optimization techniques

Path	csiph.com!xmission!news.snarked.org!border2.nntp.dca1.giganews.com!border1.nntp.dca1.giganews.com!nntp.giganews.com!news.iecc.com!.POSTED.news.iecc.com!nerds-end
From	"Rick C. Hodgin" <rick.c.hodgin@gmail.com>
Newsgroups	comp.compilers
Subject	Re: Optimization techniques
Date	Fri, 19 Apr 2019 11:48:52 -0400
Organization	Liberty Software Foundation
Lines	39
Sender	news@iecc.com
Approved	comp.compilers@iecc.com
Message-ID	<19-04-010@comp.compilers> (permalink)
References	<19-04-004@comp.compilers> <19-04-009@comp.compilers>
Mime-Version	1.0
Content-Type	text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding	8bit
Injection-Info	gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="24525"; mail-complaints-to="abuse@iecc.com"
Keywords	optimize, design
Posted-Date	19 Apr 2019 11:53:32 EDT
X-submission-address	compilers@iecc.com
X-moderator-address	compilers-request@iecc.com
X-FAQ-and-archives	http://compilers.iecc.com
Content-Language	en-US
Xref	csiph.com comp.compilers:2194

Show key headers only | View raw

On 4/19/2019 4:49 AM, Kaz Kylheku wrote:
> If you can make your language "C/C++ like" without all the undefined
> behavior looming at every corner (i.e. not actually "C/C++ like" at all
> in a significant regard), then you've dodged what is probably the number one
> optimization pitfall.

I think UB is unavoidable in any C/C++ language.  It is too low-level
for speed purposes to be bogged down with things that would prevent UB.
Even something simple like pointer use after free.  It can be difficult
to catch statically.

> For instance, don't have it so that the order of evaluation of
> function or operator arguments is unspecified. If you allow side-effects
> in expressions, specify when those effects take place in relation to
> everything else in the expression.
>
> If you have clear ordering rules, then you honor them when optimizing:
> you rearrange the user's calculation order only when it can't possibly
> make a difference to the result that is required by the defined
> order.

I do have very clear ordering rules.  I'm actually surprised to learn
that other systems do not.  I would've thought it would be absolutely
essential.

> Reordering arithmetic calculations has pitfalls. There are n! orders
> for adding together n numbers. Under floating-point, these all
> potentially return different results even if nothing overflows.
> You can't blindly rely on arithmetic identities to hold.

I think people who use floating point recognize it is not an exact
numbering system.

I have introduced native support for arbitrary precision integers
(bi) and floating point (bfp) to address this, but even then it's
still limited precision and not exact.

--
Rick C. Hodgin

Back to comp.compilers | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Optimization techniques "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-17 09:42 -0400
  Re: Optimization techniques Hans Aberg <haberg-news@telia.com> - 2019-04-17 18:11 +0200
  Re: Optimization techniques George Neuner <gneuner2@comcast.net> - 2019-04-18 04:07 -0400
    Re: Optimization techniques "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-18 11:22 -0400
      Re: Optimization techniques George Neuner <gneuner2@comcast.net> - 2019-04-19 15:48 -0400
    Re: Optimization techniques Hans Aberg <haberg-news@telia.com> - 2019-04-19 00:52 +0200
  Re: Optimization techniques Kaz Kylheku <847-115-0292@kylheku.com> - 2019-04-19 08:49 +0000
    Re: Optimization techniques "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-19 11:48 -0400
      Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-04-23 09:38 +0200
    Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-04-23 09:18 +0200
  Re: Optimization techniques Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2019-04-20 00:27 +0200
    Re: Optimization techniques "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-19 16:11 -0700
      Re: Optimization techniques Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2019-04-20 19:47 +0200
        Re: Optimization techniques "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 10:16 -0400
    Re: Optimization techniques George Neuner <gneuner2@comcast.net> - 2019-04-20 18:59 -0400
    Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-04-23 09:43 +0200
      Re: Optimization techniques Martin Ward <martin@gkc.org.uk> - 2019-04-26 20:10 +0100
        Re: Optimization techniques Kaz Kylheku <847-115-0292@kylheku.com> - 2019-04-26 21:11 +0000
        Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-04-28 17:22 +0200
          Re: Optimization techniques Gene Wirchenko <genew@telus.net> - 2019-04-30 18:07 -0700
            Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-05-01 09:03 +0200
    Re: Optimization techniques "Derek M. Jones" <derek@_NOSPAM_knosof.co.uk> - 2019-04-26 13:39 +0100
  Re: Optimization techniques rockbrentwood@gmail.com - 2019-09-26 20:35 -0700

csiph-web