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Kumba
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PostPosted: Tue Mar 29, 2005 3:07 pm    Post subject: [Wanted]: gcc-4.x gurus Reply with quote

Alrighty, I'm posting this topic to try and tap the power of the community. Under the mips arch, we're using a patch in gcc-3.4.x that adds optimization support for the R10000 processor family. The original variant of the patch was for gcc-3.0, found here: http://gcc.gnu.org/ml/gcc-patches/2001-07/msg01161.html

I managed to forward-port the patch upwards to gcc-3.4.x, and this patch can be found here:
http://dev.gentoo.org/~kumba/mips/misc/gcc-3.4.1-add_mips_march_r10k_support.patch

What we're looking for is a port of this patch to the gcc-4.x DFA format so that when we finally adopt gcc-4 in portage as mainstream, the mips arch will have available the -march=r10000 and -mtune=r10000 options. I've poked around with it myself, but lacking the deep-level compiler knowledge that the usual gcc hacker has, I haven't been able to discern heads from tails in how things got moved around in the bump from gcc-3.4.x to gcc-4.x, so I haven't had alot of luck porting this. Plus, if this gets ported in time, it can hopefully be submitted back upstream and have a chance of making it into the mainline gcc tree for inclusion in future gcc releases.

Those curious about the performance gains this offers, based on my reading, this patch allows the compiler to schedule the instructions a little differently to take advatange of some of the better parallelization the R10000 offers (such as utilizing the second ALU unit it has). As reported by the original author of the gcc-3.0 patch, he saw performance gains upwards of %15. This doesn't mean the average user of the Octane, IP28, or even IP27 systems will see a blazing increase in speed, but they may notice some things running more efficiently, given various factors ongoing at the time.

Those interested in a cursory test of the benefits this patch offers can see a thread on the Nekochan forums comparing gcc to MIPS pro here:
http://forums.nekochan.net/viewtopic.php?t=4966

If anyone succeeds in making a patch to gcc-4.x, I'll try and give it a test run in a chroot on my Octane (assuming I can get gcc-4 to even bootstrap...), and if it looks to work, tack it onto our gcc-4 beta ebuilds.


--Kumba
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--Emperor Turhan, Centauri Republic


Last edited by Kumba on Mon Jun 19, 2006 4:13 pm; edited 1 time in total
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stonent
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PostPosted: Mon Apr 11, 2005 9:00 pm    Post subject: Reply with quote

Well certainly it would be nice to see -ftree-vectorize work with MIPS SIMD. Right now only SSE/SSE2 and Altivec are supported. (This probably would require a whole lot of code to integrate into MIPS)
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Kumba
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PostPosted: Sun May 28, 2006 3:39 am    Post subject: Reply with quote

Completed patch I'm going to utilize. Not sure if It'll do anything, but it's the best I've come up with so far:
http://dev.gentoo.org/~kumba/mips/misc/gcc-4.1.0-add-march-r10k.patch

Original submission to gcc-patches:
http://gcc.gnu.org/ml/gcc-patches/2005-12/msg01590.html

If anyone sees any problems with this patch, let me know, cause it's going to go into gcc-4.1.0/4.1.1 ebuilds soonish and I'll re-submit it to gcc-patches as well.


--Kumba
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Kumba
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PostPosted: Mon Jun 19, 2006 4:13 pm    Post subject: Reply with quote

Removing from Sticky -- This issue is done
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