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Date: Fri, 08 Apr 2005 15:16:19 +0800
From: David Xu <davidxu@freebsd.org>
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To: Francois Tigeot <ftigeot@wolfpond.org>
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cc: Mike Schroll <FreeBSD@LogicX.us>
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Subject: Re: FreeBSD Port: subversion-1.1.3
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Francois Tigeot wrote:

>On Fri, Apr 08, 2005 at 09:54:04AM +0800, David Xu wrote:
>  
>
>>I heard only -O works, -O2 does not work, -Os sometimes is a higher 
>>optimization
>>level than -O2.
>>    
>>
>
>AFAIK, -Os is only a subset of -O2.
>
>-Os only includes the -O2 optimisations which don't increase code size;
>it gives generally better performance than -O2 due to a better cache
>footprint.
>
>I have found this particularly true when using VIA C3 processors.
>
>  
>
According to gcc manual:
    -Os    Optimize  for  size.  This enables all -O2 optimizations that do
              not typically increase code size.  It also performs 
further  op-
              timizations designed to reduce code size.

So the options are overlapped, and also each option has its own 
optimizations, it should
be treated that both -Os and -O2 have dangerous optimizations.

David Xu