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Date: Fri, 23 Jul 2010 17:02:38 +0800
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Subject: Re: When will the next gcc come out
From: Huang Bambo <bambo DOT huang AT gmail DOT com>
To: cygwin AT cygwin DOT com
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2010/7/23 Andy Koppe <andy DOT koppe AT gmail DOT com>:
> On 23 July 2010 09:24, Huang Bambo wrote:
>> The current gcc( 4.3.4 ) has some bug with O3 option. it will
>> optimized out some needed code in some case.
>> I meet this bug when I compile ACE library.
>> If I use O2 option, everything goes fine.
>
> Have you got any actual evidence for this being a bug in gcc rather
> than in your program? It's quite common that subtle program bugs get
> exposed differently by different optimisations. This might also be
> relevant:

It's a very simple test program:

#include <ace/Log_Msg.h>

int ACE_TMAIN( int argc, ACE_TCHAR **argv )
{
        ACE_DEBUG(( LM_DEBUG, ACE_TEXT("%D\n") ));
        return 0;
}

Gcc optimized out some code like
*fp++ =3D *format_string ++;

When I gdb to that line and "print fp", gdb reported that fp is optized out=
...

If I compile ACE library with -O2, everything become OK.

I will check if this will happen in other platform when I have time.

> http://en.wikipedia.org/wiki/Aliasing_(computing)#Conflicts_with_optimiza=
tion
>
> Andy
>
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