Date: Fri, 15 Dec 2006 12:50:08 +0100 From: Stefan Ehmann <shoesoft@gmx.net> To: freebsd-current@freebsd.org Cc: Peter Jeremy <peterjeremy@optushome.com.au>, Steve Kargl <sgk@troutmask.apl.washington.edu> Subject: Re: Let's use gcc-4.2, not 4.1 -- OpenMP Message-ID: <200612151250.10033.shoesoft@gmx.net> In-Reply-To: <458235EC.80300@samsco.org> References: <20061213192150.CF83D16A417@hub.freebsd.org> <20061215044453.GB9381@troutmask.apl.washington.edu> <458235EC.80300@samsco.org>
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On Friday 15 December 2006 06:43, Scott Long wrote: > Steve Kargl wrote: > > On Fri, Dec 15, 2006 at 02:50:30PM +1030, Daniel O'Connor wrote: > >>On Friday 15 December 2006 05:50, Scott Long wrote: > >>>Yes, the industry moves fast, but that's no reason to fool ourselves > >>>into thinking that the FSF will support GCC 4.2 a day after they release > >>>4.3 and start working on 4.4. Your point above about the lifespan of > >>>FreeBSD 7.x is a valid one, and I agree that it should be a > >>>consideration. Vendor support is a myth and should not be a > >>>consideration. > >> > >>Not to mention it is *trivial* to install a compiler using ports or > >> packages. > >> > >>If you are serious about high performance computing installing a new > >> compiler is about the lowest barrier you'll find. > > > > Actually, 4.1.x will produce much worse code than 3.4.6. > > You can search the gcc mail listings for extensive comparison > > by Clinton Whaley (the author of math/atlas) for details. > > Has this been fixed in GCC 4.2? If the FSF claims to have fixed it, > has it been actually verified? I thought that gcc 4 was supposed to > solve the world's problems with vectorization. I've been playing around with optimizations for a small cpu-intensive program (only integer, no FP) for a course some time ago and tested different gcc versions. gcc-3.4 (with -O3 -march=pentium4) won over gcc-4.0 there. My new test setup: FreeBSD 6.2-RC1 gcc version 3.4.6 [FreeBSD] 20060305 (base system) gcc version 4.1.2 20061013 (prerelease) (lang/gcc41 package) gcc version 4.2.0 20061014 (experimental) (lang/gcc42 package) CPU: AMD Athlon(TM) XP 2700+ (2166.44-MHz 686-class CPU) Instructions counted with pmcstat -C -p k7-retired-instructions Settings/Compiler | gcc-3.4 | gcc-4.1 | gcc-4.2 ----------------------------+---------+---------+--------- -O2 | 13.1bn | 13.8bn | 13.5bn -O2 -funroll-loops | 9.6bn | 9.3bn | 9.2bn -O2 -march=athlon-xp -fun.. | 9.7bn | 10.6bn | 10.7bn -O3 | 11.5bn | 9.5bn | 9.6bn -O3 -funroll-loops | 8.4bn | 9.2bn | 9.4bn -O3 -march=athlon-xp -fun.. | 8.8bn | 10.6bn | 11.1bn I'm aware that testing with a single program is not too meaningful, but it might give a hint at least.
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