Re: Why not build kernel with -O3

From: Austin S Hemmelgarn <ahferroin7@gmail.com>
To: Pengfei Yuan <0xcoolypf@gmail.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: Why not build kernel with -O3
Date: Wed, 08 Apr 2015 09:53:35 -0400	[thread overview]
Message-ID: <552532DF.7060004@gmail.com> (raw)
In-Reply-To: <CACmZjJJd0t_fSQMATN=-LJwm683+tqR90sPPAaCUCvNJ+P8MoQ@mail.gmail.com>

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On 2015-04-08 09:19, Pengfei Yuan wrote:
> 2015-04-08 20:06 GMT+08:00 Austin S Hemmelgarn <ahferroin7@gmail.com>:
>> I can't remember any off the top of my head, but it does say explicitly in
>> the GCC manual to be careful with -O3.  IIRC, most of the issues relate to
>> -O3 enabling -ffast-math (which tends to really mess with code that expects
>> strict IEEE 754 compliance), so it may not be as much of an issue for kernel
>> code.  You might look into some of the projects that use -O3 by default (I
>> think most of the Mozilla so0ftware does these days, and I know that there
>> are others, I just can't remember what right now).
>>
>
> I am afraid you are talking about -Ofast, not -O3.
> See https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html
>
> Yuan
>
You're right, I had been looking at the wrong paragraph in the info 
manual.  Sorry about any confusion.


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