From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Mon, 10 Apr 2006 16:51:10 -0700
From: Roman Shaposhnick <rvs@sun.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] Good enough approximation for ape/pcc
Message-ID: <20060410235110.GM28006@submarine>
References: <229aaef51090aa24504f7f55d106b8c2@quanstro.net>
	<b7fc9c10c9cc1ec573f332cec5ed67a9@coraid.com>
	<6.0.2.0.0.20060411100415.01cb6490@pop.monitorbm.co.nz>
	<200604102304.k3AN4vJN003576@haides.silverbrookresearch.com>
	<3e1162e60604101618u4e4ce0c1yac9f0246a116a2e5@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=koi8-r
Content-Disposition: inline
In-Reply-To: <3e1162e60604101618u4e4ce0c1yac9f0246a116a2e5@mail.gmail.com>
User-Agent: Mutt/1.4.1i
Topicbox-Message-UUID: 346423f6-ead1-11e9-9d60-3106f5b1d025

On Mon, Apr 10, 2006 at 04:18:56PM -0700, David Leimbach wrote:
> Interesting example...
>
> SomeContainer::iterator it = SomeContainerObject.begin();
>
> for (; it != SomeContainerObject.end(); ++it)
>
> is probably a lot faster than
>
> for(; it != SomeConatinerObject.end(); it++)
>
> And I'd bet that not much more than half of the so-called C++
> programmers out there in the world know why this is.

  If the punch line here is, in fact, what I think it is, then
  a good optimizing compiler should be able to make these two
  pretty close in terms of performance.

  I've been doing optimizing compilers at Sun for quite some time
  now (C/C++ and Fortran) and one thing that I constantly talk
  to our customers about is that in todays world of opaque CPU
  design they actually don't know whether 'a = a + 1;' is slower
  or faster than 'a++;'. So the best advice I can give them
  is to:

     1. Express semantics, not how to generate code
     2. Pick a compiler vendor you can trust.
     3. Make Performance Analysis part of your debugging.


Thanks,
Roman.