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Re: RFC: Optimizing for 386



On Thu, Jan 20, 2005 at 02:36:24PM +0100, Dawid Gajownik wrote:
> Dnia 01/19/2005 06:02 PM, U??ytkownik Jakub Jelinek napisa??:
> 
> >Yes, we know very well about -march and -mtune difference.
> >The current CFLAGS (for *.i386.rpm -march=i386 -mtune=pentium4) are just 
> >fine
> >for the whole distro.
> 
> And what about LDFLAGS? Has anyone been experimenting with this 
> variable? I've read those two pages:
> http://forums.gentoo.org/viewtopic.php?t=226909
> http://bugs.gentoo.org/show_bug.cgi?id=65002
> and it sounds promising - some optimizations for free :D Does it have 
> any drawbacks?

First of all, I guess for many packages it isn't trivial to propagate
LDFLAGS down.

-Wl,-O1 does only one thing in all binutils I know, particularly
use an O(nsyms^2) algorithm to optimize .hash section for minimal chain
lengths.
It is very expensive for really large shared libraries, for the largest
ones I've seen it takes an hour or more to link with this option.
Plus when the library is prelinked and used (at least mostly) as direct
dependency of prelinked programs, then -Wl,-O1 actually hurts (as it means
.hash section is bigger than necessary) instead of helping.

	Jakub


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