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List Archive: gentoo-amd64
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To: gentoo-amd64@g.o
From: Duncan <1i5t5.duncan@...>
Subject: Re: GCC-4.5.2 Has Serious Problems
Date: Fri, 1 Jul 2011 02:18:15 +0000 (UTC)
Frank Peters posted on Thu, 30 Jun 2011 21:04:29 -0400 as excerpted:

> On Fri, 01 Jul 2011 02:44:36 +0300 Nikos Chantziaras <realnc@...>
> wrote:
> 
>> And here you can read more thorough information about strict aliasing:
>> 
>>    http://labs.qt.nokia.com/2011/06/10/type-punning-and-strict-aliasing
>> 
> You've saved the day in more ways than one.
> 
> A few days ago I posted about a possible problem with a floating point
> test called the UCBTEST.  After examining the source code of this test,
> I see violations of aliasing rules throughout. It's hard to efficiently
> manipulate variables without them.
> 
> Of course, this code was written before the C99 standard and so is
> exempt.  But the use of "-fno-strict-aliasing" will apply with the
> UCBTEST as well.

Truthfully, I thought sure this was a direct follow-on to that! So I'm 
happy to see that the same cause and solutions apply.  =:^)

As I said in an earlier post, tho, expect there to be more problems like 
that with code of that age as time goes on, because they're well past the 
easy optimizations now, and into stuff like this.  So it may be wise to 
keep an eye out  and test the minor gcc version bumps with an eye toward 
such issues.  They generally put out a porting guide, etc, with the new 
version, that you can read for clues in case the tests start doing 
unexpected things again.  

(If you pay attention to flameeyes' blog, he tends to cover such things 
reasonably early on after release of a new gcc version as well, as he 
does tinderbox runs to see how bad the interaction of the new version is 
with the current gentoo ~arch tree as a whole and eventually to test that 
the latest ~arch packages are updated or patched to fix the problem, 
before that gcc version gets unmasked to ~arch.  By no means do I agree 
with everything he says, but he really is an asset to gentoo and would be 
sorely missed should one of his sick episodes make it impossible for him 
to continue, or if he simply decided he had better things to do with his 
time.  The switch to --as-needed in Gentoo's default ldflags was largely 
due to his work, explaining the issues for other devs, testing and filing 
bugs, helping with the hard cases, and in general pushing it until it 
happened, for instance, and every single gentoo user benefits from that 
in the form of less mandatory rebuilds, every time they update.  It may 
well have happened without him, but it might have taken a decade longer, 
too.  And because gentoo devs normally push those patches upstream where 
they can, that has been a benefit to the entire FLOSS community, not just 
gentoo, as well, reducing "dependency hell" for everyone.)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman



References:
GCC-4.5.2 Has Serious Problems
-- Frank Peters
Re: GCC-4.5.2 Has Serious Problems
-- Nikos Chantziaras
Re: GCC-4.5.2 Has Serious Problems
-- Nikos Chantziaras
Re: Re: GCC-4.5.2 Has Serious Problems
-- Frank Peters
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Updated Jun 28, 2012

Summary: Archive of the gentoo-amd64 mailing list.

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