Date: Tue, 25 May 1999 13:35:00 -0500 From: Dan Nelson <dnelson@emsphone.com> To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> Cc: current@FreeBSD.ORG Subject: Re: More compiler option comparisons Message-ID: <19990525133459.B17956@dan.emsphone.com> In-Reply-To: <199905251635.MAA11353@khavrinen.lcs.mit.edu>; from "Garrett Wollman" on Tue May 25 12:35:12 GMT 1999 References: <199905251635.MAA11353@khavrinen.lcs.mit.edu>
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In the last episode (May 25), Garrett Wollman said: > Just for completeness, I did one final run of HINT with just `-O' > specified (our usual default). `-O' results in significantly better > integer performance than `-O4'. (Floating-point performance is just > the opposite.) > > This suggests that compiling the world with `-O' levels higher than > one is probably a bad idea. (The generated assembly is identical from > `-O2' to `-O4'.) The `-O2' code appears to be less efficient at > register allocation; about twice as much stack temporary space is > required. -O4 doesn't exist in egcs (or it didn't a month or so ago). According to the source, -O2 enables all optimizations except -funroll-all-loops, and all -O3 does is enable -funroll-all-loops. I'd like to see separate runs, one with each -march= option (i386, i486, i586, i686), so see if those many any difference at all. -Dan To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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