Date: Fri, 17 Mar 2000 12:50:45 +0100 From: Sascha Schumann <sascha@schumann.cx> To: Doug Barton <Doug@gorean.org> Cc: freebsd-current@freebsd.org Subject: Re: gcc -Os optimisation broken (RELENG_4) Message-ID: <20000317125045.A15480@schumann.cx> In-Reply-To: <38D1CC21.B4A59808@gorean.org>; from Doug@gorean.org on Thu, Mar 16, 2000 at 10:09:37PM -0800 References: <38CF48CF.59A100D7@altavista.net> <8ap8qe$hvj$1@bigeye.rhein-neckar.de> <38D08908.C629B55E@gorean.org> <38D08ADF.9C28C61E@cvzoom.net> <38D1CC21.B4A59808@gorean.org>
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On Thu, Mar 16, 2000 at 10:09:37PM -0800, Doug Barton wrote: > Donn Miller wrote: > > > > Doug Barton wrote: > > > > > Hmm... If I have a PII (Actually celeron 300A) or a PIII, which is > > > better, 'pentium' or 'pentiumpro'? I would think the latter, but I've > > > learned not to assume where gcc is concerned. > > > > I think that 'pentium' would result in code that isn't as optimized as > > 'pentiumpro', but I've heard that 'pentium' has a lot less problems. > > > > > Also, I have heard conflicting reports as to whether compiling the > > > kernel/world with optimisations is a good thing. Anyone care to (re)open > > > that can of worms? > > > > I compile my kernel/world with -mpentium -O3 -pipe. The only problem > > I've seen so far were spurious random reboots that would occur about > > 2-3 times a month. But, that was last summer, and hasn't happened > > since. Something else must have been the culprit. (Maybe -current > > wasn't as stable last summer.) With the aforementioned CFLAGS, I have > > a pretty reliable and stable system. > > > > I've heard that -mpentiumpro can be pretty buggy, and it can actually > > result in slower code than -mpentium for certain pentium types. I > > trust plain -mpentium, as it has been very reliable for me, except for > > some compile-time errors caused by the optimization (Qt). > > In the interests of providing another datapoint, I tried my old, boring > P5 machine, and with -Os -march=pentium buildworld bombed trying to > compile cc1plus in the build tools phase. Backing off to -O worked. The > kernel was ok with -Os -march=pentium. In contrast, I've been using -Os -march=pentium during the last three months for buildworld and the kernel. Never had problems whatsoever. - Sascha To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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