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-O3 is unstable on G4?
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VanDan
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PostPosted: Tue Jul 19, 2005 1:12 pm    Post subject: -O3 is unstable on G4? Reply with quote

Greetings.

After compiling on my powerbook for close to a day now, I've come across a couple of pages that claim that I shouldn't use -O3 in my CFLAGS for a G4, as it is broken:
http://www.freehackers.org/gentoo/gccflags/flag_gcc3.html
http://linuxreviews.org/howtos/compiling/unsafe-cflags/#toc1
Interesting :)

Since I've almost completed the install, I won't start again now ... lets see what happens. Does anyone know if this advice is outdated for, say, gcc-3.4.4?

Anyway, I'll report back later with my success / failure report :)
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AaronPPC
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PostPosted: Tue Jul 19, 2005 2:28 pm    Post subject: Reply with quote

It was my understanding that -O3 is still broken. Both of those site are pretty dated, though. Thanks for doing the experiment. :)

I thought it was funny that the freehackers site says to use -O3 if you don't know which PPC you have.

Contrary to the second link, you CAN use -mabi=altivec.

--Aaron
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JoseJX
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PostPosted: Tue Jul 19, 2005 2:54 pm    Post subject: Reply with quote

-O3 was broken for G4's for a while, but to be honest, I'm not sure if it still is. I've found that compiling for size (-Os) instead seems to give more benefit on my G4 500, so I haven't tested it. If you haven't had any problems yet, I wouldn't worry about it too much. :)
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corsair
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PostPosted: Wed Jul 20, 2005 8:09 am    Post subject: Reply with quote

I am using -O3 for quite some while now (>6 month) on my PowerBook G4 and my PowerMac G5 and have had no problems. So I would declare -O3 as rock solid stable! 8)
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mikegpitt
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PostPosted: Wed Jul 20, 2005 6:23 pm    Post subject: Reply with quote

I was using -O3 and some other opts, but then switched back to the default. I never had any problems with -O3 (I switched for other reasons) and a bunch of my software is probaly still compiled with -O3 and works fine.
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VanDan
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PostPosted: Fri Jul 22, 2005 4:50 am    Post subject: Report Back Reply with quote

I'm glad to report that compiling my entire system with -O3 seems to have resulted in a perfectly stable system on my G4 Powerbook :)

The speed is also quite impressive ( not that I've benchmarked it against anything else, but still ... ). Even running xcompmgr -Ff results in a system that's quite snappy - my work PC won't do that ( Pentium 4 @ 2.6 Ghz ). Unfortunately when I run transset that changes things dramatically - not usable at all. Nothing new there I suppose.

So anyway, to those wondering if it's safe to compile with -O3 in your CFLAGS on a G4, I say it is :)
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_savage
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PostPosted: Sat Jul 30, 2005 5:46 am    Post subject: Re: Report Back Reply with quote

VanDan wrote:
So anyway, to those wondering if it's safe to compile with -O3 in your CFLAGS on a G4, I say it is :)


Hmm... nifty. So I too switch from -O2 to -O3 now and keep telling myself that it really makes a difference ;-) But thanks for trying it out!

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