Re: [gentoo-user] Re: CFLAGS "...-O3 -pipe" vs "...O2 <no pipe>"

["Francisco Rivas" <taken2k4@gmail.com>]

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Hi all..

I think what -O3 is not _dangerous_ when you know how to use, a few posts
ago someone mentioned not all of packages can be compiled using -O3, if I am
not wrong was GCC and OpenOffice.org.

The thing is: -O3 is not a _damage_ is an carefully flag to compile for some
packages..

In some webpages I people said : ".. -O3 is not used by developer because
come troubles when you want to do a debug..".

But:
 http://www.nersc.gov/vendor_docs/intel/f_ug2/dbg_opt.htm,
 http://linuxgazette.net/121/hegde.html,
http://publib.boulder.ibm.com/infocenter/macxhelp/v6v81/index.jsp?topic=/com.ibm.xlf81m.doc/pgs/ug42.htm
.

"...The following setting is the "Optimizations". You shouldn't use O3 as it
takes longer to compile, the generated code will be sometimes faster,
sometimes slower and almost always larger. For example, a program that was
compiled with the O2 level of optimization is 250KB large and is quite fast,
the same program compiled with the O3 level of optimization can take more
time to compile, produce a larger binary, depending on the code, even
500-700KB large and it can be slower or faster. Therefore, the O3
optimization level isn't recommended. Use O2 if you need the best
optimization without adding the risk of obtaining large binaries, which need
a long time to be loaded before being executed and are not always faster..."
take of http://www.softpedia.com/reviews/linux/Gentoo-Review-20543.shtml.


On 4/11/07, Bo Ørsted Andresen <bo.andresen@zlin.dk> wrote:
>
> On Wednesday 11 April 2007 12:56:43 Daniel Iliev wrote:
> > Sorry, I don't get it. Perhaps it is my poor English but I couldn't
> > understand two things:
> >  - Is -O3 supported by Gentoo or not?
>
> -O3 is supported by Gentoo.
>
> >  - What's the special thing about Gentoo ebuilds that makes -O3
> dangerous?
>
> No no. The special thing about Gentoo ebuilds is that -O3 in make.conf is
> safe
> for all packages because those packages for which -O3 isn't safe are
> replacing it with -O2 in the ebuilds (or eclasses).
>
> --
> Bo Andresen
>
>


-- 
['Cause without love I won't survive, I love you]. I

Francisco Rivas
2.6.19-gentoo-r5 x86
udev v087 gnome 2.16.2
xorg-x11-7.1 hotplug v20040923-r2
e-mail : fjrivas@uc.edu.ve
msn : taken2k4@gmail.com

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