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c.f. bug 424647
List Archive: gentoo-amd64
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To: gentoo-amd64@g.o
From: Nikos Chantziaras <realnc@...>
Subject: Re: GCC-4.5.2 Has Serious Problems
Date: Fri, 01 Jul 2011 03:11:09 +0300
On 07/01/2011 03:04 AM, Frank Peters wrote:
> On Fri, 01 Jul 2011 02:44:36 +0300
> Nikos Chantziaras<realnc@...>  wrote:
>
>>>
>>> Your code is buggy, because you're breaking C's aliasing rules. You are
>>> not allowed to use a different pointer type to dereference a variable of
>>> a different type. Doing so results in undefined behavior.
>>
>
> Well, the error occurs only within the loop structure.  If
> I manually "unroll" the loop using the same pointers there
> is no error when compiled with "O2."
>
> IOW, the problem is how the loop is optimized under -O2.

When there's "undefined behavior", it really means just that: you cannot 
make any assumptions about when the result is going to be correct and 
when not.  It might as well depend on whether it was raining yesterday.



Replies:
Re: GCC-4.5.2 Has Serious Problems
-- Duncan
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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